High-efficiency micro-leds

ABSTRACT

Disclosed herein are light emitting diodes (LEDs) having a high efficiency. A light emitting diode including an active light emitting layer within a semiconductor layer is provided. The semiconductor layer has a mesa shape. The light emitting diode also includes a substrate having a first surface on which the semiconductor layer is positioned and an outcoupling surface opposite to the first surface. Light generated by the active light emitting layer is incident on the outcoupling surface and propagates toward an optical element downstream of the outcoupling surface. The light emitting diode also includes a first anti-reflection coating adjacent to the outcoupling surface; an index-matched material between the outcoupling surface and the optical element, wherein an index of refraction of the index-matched material is greater than or equal to an index of refraction of the optical element; and/or secondary optics adjacent to the outcoupling surface.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority under 35 U.S.C. § 119 to U.S.Provisional Patent Application No. 62/651,044, filed on Mar. 30, 2018,the contents of which are hereby incorporated by reference in theirentirety.

BACKGROUND

Light emitting diodes (LEDs) convert electrical energy into opticalenergy. In semiconductor LEDs, light is usually generated throughrecombination of electrons and holes within a semiconductor layer. Achallenge in the field of LEDs is to extract as much of the emittedlight as possible toward the desired direction. Various approaches maybe used to increase the efficiency of an LED, such as adjusting theshape of the semiconductor layer, roughening the surface of thesemiconductor layer, and using additional optics to redirect or focusthe light.

Micro-LEDs are being developed for various applications in displaytechnology. A micro-LED has a very small chip size. For example, alinear dimension of the chip may be less than 50 μm or less than 10 μm.The linear dimension may be as small as 2 μm or 4 μm. However,micro-LEDs typically have a lower efficiency than large-power LEDs.While large-power LEDs may have a light extraction efficiency (LEE) ofup to 90%, micro-LEDs typically have a LEE on the order of 10% within anemission cone having an angle of 90°, and 0.5% within an emission conehaving an angle of 10°. For example, a large-power LED or a micro-LED,such as the planar LED 800 shown in FIG. 29, typically has a planar LEDLambertian pattern 830 with a full-width at half-maximum (FWHM) ofapproximately 120° and a half-width at half-maximum (HWHM) ofapproximately 60°. A vertical micro-LED, similar to the hemisphericalLED 810 shown in FIG. 29, typically has a hemispherical LED pattern 840with a HWHM greater than or equal to 60°, in which side wall emissionmay lead to bunny ears. Further, a parabolic LED 820 typically has aparabolic LED emission 850 with a more narrow profile having a HWHM lessthan 60°, and typically between 20° and 40°. Accordingly, it would beadvantageous to increase the LEE of micro-LEDs, and to provide an outputbeam with a narrower beam profile.

SUMMARY

The present disclosure generally relates to micro-LEDs having animproved efficiency. In certain embodiments, a light emitting diodeincludes an active light emitting layer within a semiconductor layer.The semiconductor layer has a mesa shape. The light emitting diode alsoincludes a substrate having a first surface on which the semiconductorlayer is positioned and an outcoupling surface opposite to the firstsurface. Light generated by the active light emitting layer is incidenton the outcoupling surface and propagates toward an optical elementdownstream of the outcoupling surface. The light emitting diode alsoincludes a first anti-reflection coating adjacent to the outcouplingsurface; an index-matched material between the outcoupling surface andthe optical element, wherein an index of refraction of the index-matchedmaterial is greater than or equal to an index of refraction of theoptical element; and/or secondary optics adjacent to the outcouplingsurface.

The mesa shape may be of planar, vertical, conical, semi-parabolic,and/or parabolic, and a base area of the mesa may be circular,rectangular, hexagonal, and/or triangular. The light emitting diode mayalso include a reflector layer on an outer surface of the mesa shape.The reflector layer may include, in order from the outer surface of themesa shape, a dielectric passivation layer, an adhesion layer, adiffusion barrier layer, and a coating layer.

The index-matched material may be butt-coupled to the optical element,and the optical element may include a waveguide. The semiconductor layermay include an n-side semiconductor layer adjacent to the substrate anda p-side semiconductor layer opposite to the active light emittinglayer.

The secondary optics may include a lens having a focal point at theactive light emitting layer. The lens may be a spherical lens or aFresnel lens. A diameter of the lens may be greater than a diameter ofthe semiconductor layer adjacent to the substrate. The lens may beetched into the outcoupling surface. The lens may have different lensshapes along a lateral direction of the lens, or a donut-like recessarea and a focal point that are configured to out-couple differentgroups of rays from the light emitting diode within an emission conehaving a half-width at half-maximum (HWHM) less than or equal to 60°.

The secondary optics may be configured to emit light having a beamprofile with a substantially top-hat shape and a half-width athalf-maximum (HWHM) less than or equal to 60°. The secondary optics mayalso include additional spherical lenses that are configured tocollimate light reflected by a facet of the mesa shape. The secondaryoptics may also include a second anti-reflection coating on a surface ofthe lens opposite to the outcoupling surface. The secondary optics mayalso include a grating etched into the outcoupling surface, the gratingmay include a linear array that reflects transverse electric (TE) lightat a different percentage than transverse magnetic (TM) light, and thelight emitting diode may provide polarized light emission.

A linear dimension of the outcoupling surface in a plane perpendicularto an emission direction of light from the outcoupling surface may beless than 60 μm. The light emitting diode may have a first lightextraction efficiency between 50% and 85% within a first emission conehaving a first angle of 90°, and a second light extraction efficiencybetween 2% and 6% within a second emission cone having an second angleof 10°.

In certain embodiments, a light emitting diode includes an active lightemitting layer within a semiconductor layer. The semiconductor layer hasa mesa shape. The light emitting diode also includes a substrate havinga first surface on which the semiconductor layer is positioned and anoutcoupling surface opposite to the first surface. The light emittingdiode also includes a reflector layer on an outer surface of the mesashape. The reflector layer induces, in order from the outer surface ofthe mesa shape, a dielectric passivation layer, a metal layer, adiffusion barrier layer, and a conformal coating layer.

A thickness of the dielectric passivation layer may be between 60 nm and80 nm, a thickness of the metal layer may be between 80 and 120 nm, athickness of the diffusion barrier layer may be between 20 and 30 nm,and a thickness of the conformal coating layer may be between 110 and140 nm.

The dielectric passivation layer may include SiN, SiO₂, HfO, AlN, and/orAlO. The metal layer may include Ag, Al, or Au, and may be configured toprovide adhesion between the dielectric passivation layer and thediffusion barrier layer. The diffusion barrier layer may include Pt, Pd,WTi, or WN. The conformal coating layer may include Au or Al. Thedielectric passivation layer and the metal layer may be configured toprevent resonant absorption losses inside the reflector layer.

The light emitting diode may also include a p-contact on a surface ofthe semiconductor layer opposite to the outcoupling surface. Thep-contact may include, in order from the surface of the semiconductorlayer, the metal layer, the diffusion barrier layer, and the coatinglayer.

The mesa shape may be parabolic, the mesa shape may have a height ofapproximately 1.5 μm, and the mesa shape may have a largest diameter ina plane parallel to the outcoupling surface of approximately 3.0 μm. Thelight emitting diode may have a first light extraction efficiencybetween 45% and 55% within a first emission cone having a first angle of90°, and a second light extraction efficiency between 2% and 3% within asecond emission cone having an second angle of 10°.

The active light emitting layer may be arranged at a focal point of themesa shape. A facet of the mesa shape may be sufficiently smooth toprevent non-radiative recombination of electrons and holes at the facet.

The light emitting diode may also include ions that are implanted in theactive light emitting layer. Different atoms may be intermixed withinthe active light emitting layer. The active light emitting layer mayinclude quantum dots. The active light emitting layer may include alateral quantum barrier. The reflector layer may have a reflectivitygreater than 80%.

This summary is neither intended to identify key or essential featuresof the claimed subject matter, nor is it intended to be used inisolation to determine the scope of the claimed subject matter. Thesubject matter should be understood by reference to appropriate portionsof the entire specification of this disclosure, any or all drawings, andeach claim. The foregoing, together with other features and examples,will be described in more detail below in the following specification,claims, and accompanying drawings. Additional details may be found inthe Appendix.

BRIEF DESCRIPTION OF THE DRAWINGS

Illustrative embodiments are described in detail below with reference tothe following figures:

FIG. 1 is a simplified block diagram of an example artificial realitysystem environment including a near-eye display, according to certainembodiments;

FIG. 2 is a perspective view of a simplified example near-eye displayincluding various sensors;

FIG. 3 is a perspective view of an example near-eye display in the formof a head-mounted display (HMD) device for implementing some of theexamples disclosed herein;

FIG. 4 is a simplified block diagram of an example electronic system ofan example near-eye display for implementing some of the examplesdisclosed herein;

FIG. 5 is a cross sectional view of an example of a micro-LED, accordingto one or more embodiments;

FIG. 6A shows a comparison of experimental data and simulated data forthe operating voltage (V_(op)) and the light output power (LOP) of amicro-LED emitting green light;

FIG. 6B shows a comparison of experimental data and simulated data forthe external quantum efficiency (EQE) of a micro-LED emitting greenlight, along with the simulated percentage of surface recombination;

FIG. 7A shows additional comparisons of experimental data withsimulation data for a micro-LED emitting green light;

FIG. 7B shows simulated internal quantum efficiency (IQE) data andsimulated junction temperature data for a micro-LED emitting greenlight;

FIG. 8A shows an example of a micro-LED according to one or moreembodiments;

FIG. 8B shows simulated LEE data versus angle for the green micro-LEDshown in FIG. 8A;

FIGS. 9A-9C show various examples of green micro-LEDs having differentmesa shapes from conical to parabolic;

FIGS. 10A-10C show various examples of green micro-LEDs having differentreflector layers;

FIGS. 11A and 11B show wave optic calculations, including coherenteffects, of reflection coefficients versus incident angle of light ofdifferent examples of green micro-LEDs;

FIGS. 12A-12C show various examples of green micro-LEDs having differentcomponents on the outcoupling surface to optimize the LEE and the beamprofile;

FIGS. 13A-13C show various examples of red micro-LEDs having differentcomponents on the outcoupling surface to optimize the LEE and the beamprofile;

FIGS. 14A and 14B show the effects of incorporating an index-matchedmaterial between the outcoupling surface and the optical element for agreen micro-LED;

FIGS. 15A-15C show various examples of red micro-LEDs having differentsecondary optics to optimize the LEE and the beam profile;

FIGS. 16A and 16B show an example of a green micro-LED having secondaryoptics to optimize the LEE and the beam profile;

FIGS. 17A and 17B show examples of red and green micro-LEDs havingsecondary optics to optimize the LEE and the beam profile;

FIGS. 18A-18H show examples of a red micro-LED having secondary opticsto optimize the LEE and the beam profile;

FIGS. 19A and 19B show examples of red and green micro-LEDs havingsecondary optics to optimize the LEE and the beam profile;

FIGS. 20A and 20B show an example of a green micro-LED that emitspolarized light, based on FDTD-Calculations combined with opticalRay-tracing simulations of the optics in micro-LEDs;

FIGS. 21A and 21B show the reflection coefficient as a function of anglefor reflection layer designs of micro-LED configurations that can emitpolarized light;

FIG. 22A shows an example of a micro-LED with a mesa having anon-rotationally symmetric elliptical base with a parabolic mesa shape;

FIG. 22B shows an example of a mesa having a planar shape;

FIG. 22C shows an example of a triangular mesa having a vertical andconical shape;

FIG. 22D shows an example of a rectangular base shape that may be usedin a micro-LED;

FIGS. 23A-23C show the external quantum efficiency (EQE) and the surfacerecombination for different non-radiative recombination rates in a greenmicro-LED;

FIG. 24A shows an example of a red micro-LED;

FIG. 24B shows the simulated surface recombination velocity at the mesafacet for a red micro-LED in comparison to blue and green micro-LEDs;

FIGS. 25A-25C show a comparison of the EQE and surface recombinationlosses for untreated green, blue, and red micro-LEDs;

FIGS. 26A-26C show a comparison of the EQE and surface recombinationlosses for treated green, blue, and red micro-LEDs;

FIGS. 27A-27C show examples of different methods like quantum well(QW)-intermixing for reducing the surface recombination by reducing thelateral electron-hole (e-h) diffusion to the mesa facet inside theactive light emitting area;

FIGS. 28A and 28B show an example of a method of reducing the lateralcurrent spreading by performing lateral ion implantation for a definedcurrent aperture; and

FIG. 29 shows a comparison of far-field emission patterns for differentLEDs.

DETAILED DESCRIPTION

In the following description, for the purposes of explanation, specificdetails are set forth in order to provide a thorough understanding ofexamples of the disclosure. However, it will be apparent that variousexamples may be practiced without these specific details. For example,devices, systems, structures, assemblies, methods, and other componentsmay be shown as components in block diagram form in order not to obscurethe examples in unnecessary detail. In other instances, well-knowndevices, processes, systems, structures, and techniques may be shownwithout necessary detail in order to avoid obscuring the examples. Thefigures and description are not intended to be restrictive. The termsand expressions that have been employed in this disclosure are used asterms of description and not of limitation, and there is no intention inthe use of such terms and expressions of excluding any equivalents ofthe features shown and described or portions thereof.

As used herein, ultraviolet (UV) light may refer to light with awavelength between about 100 nm and about 440 nm. Visible light mayrefer to light with a wavelength between about 380 nm and about 750 nm.More specifically, blue light may refer to light with a wavelengthbetween about 440 nm and about 495 nm. Green light may refer to lightwith a wavelength between about 495 nm and about 570 nm. Red light mayrefer to light with a wavelength between about 580 nm and about 750 nm.Near infrared (NIR) light may refer to light with a wavelength betweenabout 750 nm and about 2500 nm.

As used herein, a reflector for a wavelength range may refer to anoptical device that can reflect at least 20%, at least 50%, at least70%, or more of incident light in the wavelength range. Some reflectorsmay reflect less than 20%, less than 10%, less than 5%, less than 1%, orless of incident light outside the working wavelength range of thereflectors. The reflectivity may be represented by either aphoto-optically weighted or an unweighted average reflectivity over awavelength range, an angular range of incident beam angle to surfacenormal, or the lowest reflectivity over a wavelength range. For example,a reflector may include a mirror having metallic coatings or dielectricthin films, a distributed Bragg reflector (DBR), or a metamorphic layer.

As used herein, a micro-LED may refer to an LED that has a chip sizewith a linear dimension of the chip that is less than 50 μm, less than20 μm, or less than 10 μm. For example, the linear dimension may be assmall as 2 μm or 4 μm. However, the disclosure herein is not limited tomicro-LEDs, and may also be applied to mini-LEDs or large-power LEDs.

The micro-LEDs described herein may be used in conjunction with varioustechnologies, such as an artificial reality system. Artificial realityis a form of reality that has been adjusted in some manner beforepresentation to a user, which may include, e.g., a virtual reality (VR),an augmented reality (AR), a mixed reality (MR), a hybrid reality, orsome combination and/or derivatives thereof. Artificial reality contentmay include completely generated content or generated content combinedwith captured (e.g., real-world) content. The artificial reality contentmay include video, audio, haptic feedback, or some combination thereof,and any of which may be presented in a single channel or in multiplechannels (such as stereo video that produces a three-dimensional effectto the viewer). Additionally, in some embodiments, artificial realitymay also be associated with applications, products, accessories,services, or some combination thereof, that are used to, e.g., createcontent in an artificial reality and/or are otherwise used in (e.g.,perform activities in) an artificial reality. The artificial realitysystem that provides the artificial reality content may be implementedon various platforms, including a head-mounted display (HMD) connectedto a host computer system, a standalone HMD, a mobile device orcomputing system, or any other hardware platform capable of providingartificial reality content to one or more viewers.

An artificial reality system, such as a virtual reality (VR), augmentedreality (AR), or mixed reality (MR) system, may include a near-eyedisplay (e.g., a headset or a pair of glasses) configured to presentcontent to a user via an electronic or optic display and, in some cases,may also include a console configured to generate content forpresentation to the user and to provide the generated content to thenear-eye display for presentation. To improve user interaction withpresented content, the console may modify or generate content based on alocation where the user is looking, which may be determined by trackingthe user's eye. Tracking the eye may include tracking the positionand/or shape of the pupil of the eye, and/or the rotational position(gaze direction) of the eye. To track the eye, the near-eye display mayilluminate a surface of the user's eye using light sources mounted to orwithin the near-eye display. An imaging device (e.g., a camera) includedin the near-eye display may then capture light reflected by varioussurfaces of the user's eye. Light that is reflected specularly off thecornea of the user's eye may result in “glints” in the captured image.One way to illuminate the eye to see the pupil as well as the glints isto use a two-dimensional (2D) array of light-emitting diodes (LEDs).These LEDs may be placed at the periphery of the user's field of view(e.g., along the circumference of the viewing optics). Techniques suchas a centroiding algorithm may be used to accurately determine thelocations of the glints on the eye in the captured image, and therotational position (e.g., the gaze direction) of the eye may then bedetermined based on the locations of the glints relative to a knownfeature of the eye (e.g., the center of the pupil) within the capturedimage.

FIG. 1 is a simplified block diagram of an example artificial realitysystem environment 100 including a near-eye display 120, in accordancewith certain embodiments. Artificial reality system environment 100shown in FIG. 1 may include near-eye display 120, an external imagingdevice 150, and an input/output interface 140 that are each coupled to aconsole 110. While FIG. 1 shows example artificial reality systemenvironment 100 including one near-eye display 120, one external imagingdevice 150, and one input/output interface 140, any number of thesecomponents may be included in artificial reality system environment 100,or any of the components may be omitted. For example, there may bemultiple near-eye displays 120 monitored by one or more external imagingdevices 150 in communication with console 110. In alternativeconfigurations, different or additional components may be included inartificial reality system environment 100.

Near-eye display 120 may be a head-mounted display that presents contentto a user. Examples of content presented by near-eye display 120 includeone or more of images, videos, audios, or some combination thereof. Insome embodiments, audio may be presented via an external device (e.g.,speakers and/or headphones) that receives audio information fromnear-eye display 120, console 110, or both, and presents audio databased on the audio information. Near-eye display 120 may include one ormore rigid bodies, which may be rigidly or non-rigidly coupled to eachother. A rigid coupling between rigid bodies may cause the coupled rigidbodies to act as a single rigid entity. A non-rigid coupling betweenrigid bodies may allow the rigid bodies to move relative to each other.In various embodiments, near-eye display 120 may be implemented in anysuitable form factor, including a pair of glasses. Some embodiments ofnear-eye display 120 are further described below with respect to FIGS. 2and 3. Additionally, in various embodiments, the functionality describedherein may be used in a headset that combines images of an environmentexternal to near-eye display 120 and content received from console 110,or from any other console generating and providing content to a user.Therefore, near-eye display 120, and methods for eye tracking describedherein, may augment images of a physical, real-world environmentexternal to near-eye display 120 with generated content (e.g., images,video, sound, etc.) to present an augmented reality to a user.

In various embodiments, near-eye display 120 may include one or more ofdisplay electronics 122, display optics 124, one or more locators 126,one or more position sensors 128, an eye-tracking unit 130, and aninertial measurement unit (IMU) 132. Near-eye display 120 may omit anyof these elements or include additional elements in various embodiments.Additionally, in some embodiments, near-eye display 120 may includeelements combining the function of various elements described inconjunction with FIG. 1.

Display electronics 122 may display images to the user according to datareceived from console 110. In various embodiments, display electronics122 may include one or more display panels, such as a liquid crystaldisplay (LCD), an organic light emitting diode (OLED) display, amicro-LED display, an active-matrix OLED display (AMOLED), a transparentOLED display (TOLED), or some other display. For example, in oneimplementation of near-eye display 120, display electronics 122 mayinclude a front TOLED panel, a rear display panel, and an opticalcomponent (e.g., an attenuator, polarizer, or diffractive or spectralfilm) between the front and rear display panels. Display electronics 122may include sub-pixels to emit light of a predominant color such as red,green, blue, white, or yellow. In some implementations, displayelectronics 122 may display a 3D image through stereo effects producedby two-dimensional panels to create a subjective perception of imagedepth. For example, display electronics 122 may include a left displayand a right display positioned in front of a user's left eye and righteye, respectively. The left and right displays may present copies of animage shifted horizontally relative to each other to create astereoscopic effect (i.e., a perception of image depth by a user viewingthe image).

In certain embodiments, display optics 124 may display image contentoptically (e.g., using optical waveguides and couplers), or magnifyimage light received from display electronics 122, correct opticalerrors associated with the image light, and present the corrected imagelight to a user of near-eye display 120. In various embodiments, displayoptics 124 may include one or more optical elements. Example opticalelements may include a substrate, optical waveguides, an aperture, aFresnel lens, a convex lens, a concave lens, a filter, or any othersuitable optical element that may affect image light emitted fromdisplay electronics 122. Display optics 124 may include a combination ofdifferent optical elements as well as mechanical couplings to maintainrelative spacing and orientation of the optical elements in thecombination. One or more optical elements in display optics 124 may havean optical coating, such as an anti-reflective coating, a reflectivecoating, a filtering coating, or a combination of different opticalcoatings.

Magnification of the image light by display optics 124 may allow displayelectronics 122 to be physically smaller, weigh less, and consume lesspower than larger displays. Additionally, magnification may increase afield of view of the displayed content. In some embodiments, displayoptics 124 may have an effective focal length larger than the spacingbetween display optics 124 and display electronics 122 to magnify imagelight projected by display electronics 122. The amount of magnificationof image light by display optics 124 may be adjusted by adding orremoving optical elements from display optics 124.

Display optics 124 may be designed to correct one or more types ofoptical errors, such as two-dimensional optical errors,three-dimensional optical errors, or a combination thereof.Two-dimensional errors may include optical aberrations that occur in twodimensions. Example types of two-dimensional errors may include barreldistortion, pincushion distortion, longitudinal chromatic aberration,and transverse chromatic aberration. Three-dimensional errors mayinclude optical errors that occur in three dimensions. Example types ofthree-dimensional errors may include spherical aberration, comaticaberration, field curvature, and astigmatism. In some embodiments,content provided to display electronics 122 for display may bepre-distorted, and display optics 124 may correct the distortion when itreceives image light from display electronics 122 generated based on thepre-distorted content.

Locators 126 may be objects located in specific positions on near-eyedisplay 120 relative to one another and relative to a reference point onnear-eye display 120. Console 110 may identify locators 126 in imagescaptured by external imaging device 150 to determine the artificialreality headset's position, orientation, or both. A locator 126 may be alight emitting diode (LED), a corner cube reflector, a reflectivemarker, a type of light source that contrasts with an environment inwhich near-eye display 120 operates, or some combinations thereof. Inembodiments where locators 126 are active components (e.g., LEDs orother types of light emitting devices), locators 126 may emit light inthe visible band (e.g., about 380 nm to 750 nm), in the infrared (IR)band (e.g., about 750 nm to 1 mm), in the ultraviolet band (e.g., about10 nm to about 380 nm), in another portion of the electromagneticspectrum, or in any combination of portions of the electromagneticspectrum.

In some embodiments, locators 126 may be located beneath an outersurface of near-eye display 120. A portion of near-eye display 120between a locator 126 and an entity external to near-eye display 120(e.g., external imaging device 150, a user viewing the outer surface ofnear-eye display 120) may be transparent to the wavelengths of lightemitted or reflected by locators 126 or is thin enough to notsubstantially attenuate the light emitted or reflected by locators 126.In some embodiments, the outer surface or other portions of near-eyedisplay 120 may be opaque in the visible band, but is transparent in theIR band, and locators 126 may be under the outer surface and may emitlight in the IR band.

External imaging device 150 may generate slow calibration data based oncalibration parameters received from console 110. Slow calibration datamay include one or more images showing observed positions of locators126 that are detectable by external imaging device 150. External imagingdevice 150 may include one or more cameras, one or more video cameras,any other device capable of capturing images including one or more oflocators 126, or some combinations thereof. Additionally, externalimaging device 150 may include one or more filters (e.g., to increasesignal to noise ratio). External imaging device 150 may be configured todetect light emitted or reflected from locators 126 in a field of viewof external imaging device 150. In embodiments where locators 126include passive elements (e.g., retroreflectors), external imagingdevice 150 may include a light source that illuminates some or all oflocators 126, which may retro-reflect the light to the light source inexternal imaging device 150. Slow calibration data may be communicatedfrom external imaging device 150 to console 110, and external imagingdevice 150 may receive one or more calibration parameters from console110 to adjust one or more imaging parameters (e.g., focal length, focus,frame rate, sensor temperature, shutter speed, aperture, etc.).

Position sensors 128 may generate one or more measurement signals inresponse to motion of near-eye display 120. Examples of position sensors128 may include accelerometers, gyroscopes, magnetometers, othermotion-detecting or error-correcting sensors, or some combinationsthereof. For example, in some embodiments, position sensors 128 mayinclude multiple accelerometers to measure translational motion (e.g.,forward/back, up/down, or left/right) and multiple gyroscopes to measurerotational motion (e.g., pitch, yaw, or roll). In some embodiments,various position sensors may be oriented orthogonally to each other.

IMU 132 may be an electronic device that generates fast calibration databased on measurement signals received from one or more of positionsensors 128. Position sensors 128 may be located external to IMU 132,internal to IMU 132, or some combination thereof. Based on the one ormore measurement signals from one or more position sensors 128, IMU 132may generate fast calibration data indicating an estimated position ofnear-eye display 120 relative to an initial position of near-eye display120. For example, IMU 132 may integrate measurement signals receivedfrom accelerometers over time to estimate a velocity vector andintegrate the velocity vector over time to determine an estimatedposition of a reference point on near-eye display 120. Alternatively,IMU 132 may provide the sampled measurement signals to console 110,which may determine the fast calibration data. While the reference pointmay generally be defined as a point in space, in various embodiments,the reference point may also be defined as a point within near-eyedisplay 120 (e.g., a center of IMU 132).

Eye-tracking unit 130 may include one or more imaging devices configuredto capture eye tracking data, which an eye-tracking module 118 inconsole 110 may use to track the user's eye. Eye tracking data may referto data output by eye-tracking unit 130. Example eye tracking data mayinclude images captured by eye-tracking unit 130 or information derivedfrom the images captured by eye-tracking unit 130. Eye tracking mayrefer to determining an eye's position, including orientation andlocation of the eye, relative to near-eye display 120. For example,eye-tracking module 118 may output the eye's pitch and yaw based onimages of the eye captured by eye-tracking unit 130. In variousembodiments, eye-tracking unit 130 may measure electromagnetic energyreflected by the eye and communicate the measured electromagnetic energyto eye-tracking module 118, which may then determine the eye's positionbased on the measured electromagnetic energy. For example, eye-trackingunit 130 may measure electromagnetic waves such as visible light,infrared light, radio waves, microwaves, waves in any other part of theelectromagnetic spectrum, or a combination thereof reflected by an eyeof a user.

Eye-tracking unit 130 may include one or more eye-tracking systems. Aneye-tracking system may include an imaging system to image one or moreeyes and may optionally include a light emitter, which may generatelight that is directed to an eye such that light reflected by the eyemay be captured by the imaging system. For example, eye-tracking unit130 may include a coherent light source (e.g., a laser diode) emittinglight in the visible spectrum or infrared spectrum, and a cameracapturing the light reflected by the user's eye. As another example,eye-tracking unit 130 may capture reflected radio waves emitted by aminiature radar unit. Eye-tracking unit 130 may use low-power lightemitters that emit light at frequencies and intensities that would notinjure the eye or cause physical discomfort. Eye-tracking unit 130 maybe arranged to increase contrast in images of an eye captured byeye-tracking unit 130 while reducing the overall power consumed byeye-tracking unit 130 (e.g., reducing power consumed by a light emitterand an imaging system included in eye-tracking unit 130). For example,in some implementations, eye-tracking unit 130 may consume less than 100milliwatts of power.

In some embodiments, eye-tracking unit 130 may include one light emitterand one camera to track each of the user's eyes. Eye-tracking unit 130may also include different eye-tracking systems that operate together toprovide improved eye tracking accuracy and responsiveness. For example,eye-tracking unit 130 may include a fast eye-tracking system with a fastresponse time and a slow eye-tracking system with a slower responsetime. The fast eye-tracking system may frequently measure an eye tocapture data used by eye-tracking module 118 to determine the eye'sposition relative to a reference eye position. The slow eye-trackingsystem may independently measure the eye to capture data used byeye-tracking module 118 to determine the reference eye position withoutreference to a previously determined eye position. Data captured by theslow eye-tracking system may allow eye-tracking module 118 to determinethe reference eye position with greater accuracy than the eye's positiondetermined from data captured by the fast eye-tracking system. Invarious embodiments, the slow eye-tracking system may provideeye-tracking data to eye-tracking module 118 at a lower frequency thanthe fast eye-tracking system. For example, the slow eye-tracking systemmay operate less frequently or have a slower response time to conservepower.

Eye-tracking unit 130 may be configured to estimate the orientation ofthe user's eye. The orientation of the eye may correspond to thedirection of the user's gaze within near-eye display 120. Theorientation of the user's eye may be defined as the direction of thefoveal axis, which is the axis between the fovea (an area on the retinaof the eye with the highest concentration of photoreceptors) and thecenter of the eye's pupil. In general, when a user's eyes are fixed on apoint, the foveal axes of the user's eyes intersect that point. Thepupillary axis of an eye may be defined as the axis that passes throughthe center of the pupil and is perpendicular to the corneal surface. Ingeneral, even though the pupillary axis and the foveal axis intersect atthe center of the pupil, the pupillary axis may not directly align withthe foveal axis. For example, the orientation of the foveal axis may beoffset from the pupillary axis by approximately −1° to 8° laterally andabout ±4° vertically. Because the foveal axis is defined according tothe fovea, which is located in the back of the eye, the foveal axis maybe difficult or impossible to measure directly in some eye trackingembodiments. Accordingly, in some embodiments, the orientation of thepupillary axis may be detected and the foveal axis may be estimatedbased on the detected pupillary axis.

In general, the movement of an eye corresponds not only to an angularrotation of the eye, but also to a translation of the eye, a change inthe torsion of the eye, and/or a change in the shape of the eye.Eye-tracking unit 130 may also be configured to detect the translationof the eye, which may be a change in the position of the eye relative tothe eye socket. In some embodiments, the translation of the eye may notbe detected directly, but may be approximated based on a mapping from adetected angular orientation. Translation of the eye corresponding to achange in the eye's position relative to the eye-tracking unit may alsobe detected. Translation of this type may occur, for example, due to ashift in the position of near-eye display 120 on a user's head.Eye-tracking unit 130 may also detect the torsion of the eye and therotation of the eye about the pupillary axis. Eye-tracking unit 130 mayuse the detected torsion of the eye to estimate the orientation of thefoveal axis from the pupillary axis. Eye-tracking unit 130 may alsotrack a change in the shape of the eye, which may be approximated as askew or scaling linear transform or a twisting distortion (e.g., due totorsional deformation). Eye-tracking unit 130 may estimate the fovealaxis based on some combinations of the angular orientation of thepupillary axis, the translation of the eye, the torsion of the eye, andthe current shape of the eye.

In some embodiments, eye-tracking unit 130 may include multiple emittersor at least one emitter that can project a structured light pattern onall portions or a portion of the eye. The structured light pattern maybe distorted due to the shape of the eye when viewed from an offsetangle. Eye-tracking unit 130 may also include at least one camera thatmay detect the distortions (if any) of the structured light patternprojected onto the eye. The camera may be oriented on a different axisto the eye than the emitter. By detecting the deformation of thestructured light pattern on the surface of the eye, eye-tracking unit130 may determine the shape of the portion of the eye being illuminatedby the structured light pattern. Therefore, the captured distorted lightpattern may be indicative of the 3D shape of the illuminated portion ofthe eye. The orientation of the eye may thus be derived from the 3Dshape of the illuminated portion of the eye. Eye-tracking unit 130 canalso estimate the pupillary axis, the translation of the eye, thetorsion of the eye, and the current shape of the eye based on the imageof the distorted structured light pattern captured by the camera.

Near-eye display 120 may use the orientation of the eye to, e.g.,determine an inter-pupillary distance (IPD) of the user, determine gazedirection, introduce depth cues (e.g., blur image outside of the user'smain line of sight), collect heuristics on the user interaction in theVR media (e.g., time spent on any particular subject, object, or frameas a function of exposed stimuli), some other functions that are basedin part on the orientation of at least one of the user's eyes, or somecombination thereof. Because the orientation may be determined for botheyes of the user, eye-tracking unit 130 may be able to determine wherethe user is looking. For example, determining a direction of a user'sgaze may include determining a point of convergence based on thedetermined orientations of the user's left and right eyes. A point ofconvergence may be the point where the two foveal axes of the user'seyes intersect (or the nearest point between the two axes). Thedirection of the user's gaze may be the direction of a line passingthrough the point of convergence and the mid-point between the pupils ofthe user's eyes.

Input/output interface 140 may be a device that allows a user to sendaction requests to console 110. An action request may be a request toperform a particular action. For example, an action request may be tostart or to end an application or to perform a particular action withinthe application. Input/output interface 140 may include one or moreinput devices. Example input devices may include a keyboard, a mouse, agame controller, a glove, a button, a touch screen, or any othersuitable device for receiving action requests and communicating thereceived action requests to console 110. An action request received bythe input/output interface 140 may be communicated to console 110, whichmay perform an action corresponding to the requested action. In someembodiments, input/output interface 140 may provide haptic feedback tothe user in accordance with instructions received from console 110. Forexample, input/output interface 140 may provide haptic feedback when anaction request is received, or when console 110 has performed arequested action and communicates instructions to input/output interface140.

Console 110 may provide content to near-eye display 120 for presentationto the user in accordance with information received from one or more ofexternal imaging device 150, near-eye display 120, and input/outputinterface 140. In the example shown in FIG. 1, console 110 may includean application store 112, a headset tracking module 114, a virtualreality engine 116, and eye-tracking module 118. Some embodiments ofconsole 110 may include different or additional modules than thosedescribed in conjunction with FIG. 1. Functions further described belowmay be distributed among components of console 110 in a different mannerthan is described here.

In some embodiments, console 110 may include a processor and anon-transitory computer-readable storage medium storing instructionsexecutable by the processor. The processor may include multipleprocessing units executing instructions in parallel. Thecomputer-readable storage medium may be any memory, such as a hard diskdrive, a removable memory, or a solid-state drive (e.g., flash memory ordynamic random access memory (DRAM)). In various embodiments, themodules of console 110 described in conjunction with FIG. 1 may beencoded as instructions in the non-transitory computer-readable storagemedium that, when executed by the processor, cause the processor toperform the functions further described below.

Application store 112 may store one or more applications for executionby console 110. An application may include a group of instructions that,when executed by a processor, generates content for presentation to theuser. Content generated by an application may be in response to inputsreceived from the user via movement of the user's eyes or inputsreceived from the input/output interface 140. Examples of theapplications may include gaming applications, conferencing applications,video playback application, or other suitable applications.

Headset tracking module 114 may track movements of near-eye display 120using slow calibration information from external imaging device 150. Forexample, headset tracking module 114 may determine positions of areference point of near-eye display 120 using observed locators from theslow calibration information and a model of near-eye display 120.Headset tracking module 114 may also determine positions of a referencepoint of near-eye display 120 using position information from the fastcalibration information. Additionally, in some embodiments, headsettracking module 114 may use portions of the fast calibrationinformation, the slow calibration information, or some combinationthereof, to predict a future location of near-eye display 120. Headsettracking module 114 may provide the estimated or predicted futureposition of near-eye display 120 to VR engine 116.

Headset tracking module 114 may calibrate the artificial reality systemenvironment 100 using one or more calibration parameters, and may adjustone or more calibration parameters to reduce errors in determining theposition of near-eye display 120. For example, headset tracking module114 may adjust the focus of external imaging device 150 to obtain a moreaccurate position for observed locators on near-eye display 120.Moreover, calibration performed by headset tracking module 114 may alsoaccount for information received from IMU 132. Additionally, if trackingof near-eye display 120 is lost (e.g., external imaging device 150 losesline of sight of at least a threshold number of locators 126), headsettracking module 114 may re-calibrate some or all of the calibrationparameters.

VR engine 116 may execute applications within artificial reality systemenvironment 100 and receive position information of near-eye display120, acceleration information of near-eye display 120, velocityinformation of near-eye display 120, predicted future positions ofnear-eye display 120, or some combination thereof from headset trackingmodule 114. VR engine 116 may also receive estimated eye position andorientation information from eye-tracking module 118. Based on thereceived information, VR engine 116 may determine content to provide tonear-eye display 120 for presentation to the user. For example, if thereceived information indicates that the user has looked to the left, VRengine 116 may generate content for near-eye display 120 that mirrorsthe user's eye movement in a virtual environment. Additionally, VRengine 116 may perform an action within an application executing onconsole 110 in response to an action request received from input/outputinterface 140, and provide feedback to the user indicating that theaction has been performed. The feedback may be visual or audiblefeedback via near-eye display 120 or haptic feedback via input/outputinterface 140.

Eye-tracking module 118 may receive eye-tracking data from eye-trackingunit 130 and determine the position of the user's eye based on the eyetracking data. The position of the eye may include an eye's orientation,location, or both relative to near-eye display 120 or any elementthereof. Because the eye's axes of rotation change as a function of theeye's location in its socket, determining the eye's location in itssocket may allow eye-tracking module 118 to more accurately determinethe eye's orientation.

In some embodiments, eye-tracking unit 130 may output eye-tracking dataincluding images of the eye, and eye-tracking module 118 may determinethe eye's position based on the images. For example, eye-tracking module118 may store a mapping between images captured by eye-tracking unit 130and eye positions to determine a reference eye position from an imagecaptured by eye-tracking unit 130. Alternatively or additionally,eye-tracking module 118 may determine an updated eye position relativeto a reference eye position by comparing an image from which thereference eye position is determined to an image from which the updatedeye position is to be determined. Eye-tracking module 118 may determineeye position using measurements from different imaging devices or othersensors. For example, as described above, eye-tracking module 118 mayuse measurements from a slow eye-tracking system to determine areference eye position, and then determine updated positions relative tothe reference eye position from a fast eye-tracking system until a nextreference eye position is determined based on measurements from the sloweye-tracking system.

Eye-tracking module 118 may also determine eye calibration parameters toimprove precision and accuracy of eye tracking. Eye calibrationparameters may include parameters that may change whenever a user donsor adjusts near-eye display 120. Example eye calibration parameters mayinclude an estimated distance between a component of eye-tracking unit130 and one or more parts of the eye, such as the eye's center, pupil,cornea boundary, or a point on the surface of the eye. Other example eyecalibration parameters may be specific to a particular user and mayinclude an estimated average eye radius, an average corneal radius, anaverage sclera radius, a map of features on the eye surface, and anestimated eye surface contour. In embodiments where light from theoutside of near-eye display 120 may reach the eye (as in some augmentedreality applications), the calibration parameters may include correctionfactors for intensity and color balance due to variations in light fromthe outside of near-eye display 120. Eye-tracking module 118 may use eyecalibration parameters to determine whether the measurements captured byeye-tracking unit 130 would allow eye-tracking module 118 to determinean accurate eye position (also referred to herein as “validmeasurements”). Invalid measurements, from which eye-tracking module 118may not be able to determine an accurate eye position, may be caused bythe user blinking, adjusting the headset, or removing the headset,and/or may be caused by near-eye display 120 experiencing greater than athreshold change in illumination due to external light.

FIG. 2 is a perspective view of a simplified example near-eye display200 including various sensors. Near-eye display 200 may be a specificimplementation of near-eye display 120 of FIG. 1, and may be configuredto operate as a virtual reality display, an augmented reality display,and/or a mixed reality display. Near-eye display 200 may include a frame205 and a display 210. Display 210 may be configured to present contentto a user. In some embodiments, display 210 may include displayelectronics and/or display optics. For example, as described above withrespect to near-eye display 120 of FIG. 1, display 210 may include anLCD display panel, an LED display panel, or an optical display panel(e.g., a waveguide display assembly).

Near-eye display 200 may further include various sensors 250 a, 250 b,250 c, 250 d, and 250 e on or within frame 205. In some embodiments,sensors 250 a-250 e may include one or more depth sensors, motionsensors, position sensors, inertial sensors, or ambient light sensors.In some embodiments, sensors 250 a-250 e may include one or more imagesensors configured to generate image data representing different fieldsof views in different directions. In some embodiments, sensors 250 a-250e may be used as input devices to control or influence the displayedcontent of near-eye display 200, and/or to provide an interactiveVR/AR/MR experience to a user of near-eye display 200. In someembodiments, sensors 250 a-250 e may also be used for stereoscopicimaging.

In some embodiments, near-eye display 200 may further include one ormore illuminators 230 to project light into the physical environment.The projected light may be associated with different frequency bands(e.g., visible light, infra-red light, ultra-violet light, etc.), andmay serve various purposes. For example, illuminator(s) 230 may projectlight in a dark environment (or in an environment with low intensity ofinfra-red light, ultra-violet light, etc.) to assist sensors 250 a-250 ein capturing images of different objects within the dark environment. Insome embodiments, illuminator(s) 230 may be used to project certainlight pattern onto the objects within the environment. In someembodiments, illuminator(s) 230 may be used as locators, such aslocators 126 described above with respect to FIG. 1.

In some embodiments, near-eye display 200 may also include ahigh-resolution camera 240. Camera 240 may capture images of thephysical environment in the field of view. The captured images may beprocessed, for example, by a virtual reality engine (e.g., virtualreality engine 116 of FIG. 1) to add virtual objects to the capturedimages or modify physical objects in the captured images, and theprocessed images may be displayed to the user by display 210 for AR orMR applications.

FIG. 3 is a perspective view of an example near-eye display in the formof a head-mounted display (HMD) device 300 for implementing some of theexample near-eye displays (e.g., near-eye display 120) disclosed herein.HMD device 300 may be a part of, e.g., a virtual reality (VR) system, anaugmented reality (AR) system, a mixed reality (MR) system, or somecombinations thereof. HMD device 300 may include a body 320 and a headstrap 330. FIG. 3 shows a top side 323, a front side 325, and a rightside 327 of body 320 in the perspective view. Head strap 330 may have anadjustable or extendible length. There may be a sufficient space betweenbody 320 and head strap 330 of HMD device 300 for allowing a user tomount HMD device 300 onto the user's head. In various embodiments, HMDdevice 300 may include additional, fewer, or different components. Forexample, in some embodiments, HMD device 300 may include eyeglasstemples and temples tips rather than head strap 330.

HMD device 300 may present to a user media including virtual and/oraugmented views of a physical, real-world environment withcomputer-generated elements. Examples of the media presented by HMDdevice 300 may include images (e.g., two-dimensional (2D) orthree-dimensional (3D) images), videos (e.g., 2D or 3D videos), audio,or some combinations thereof. The images and videos may be presented toeach eye of the user by one or more display assemblies (not shown inFIG. 3) enclosed in body 320 of HMD device 300. In various embodiments,the one or more display assemblies may include a single electronicdisplay panel or multiple electronic display panels (e.g., one displaypanel for each eye of the user). Examples of the electronic displaypanel(s) may include, for example, a liquid crystal display (LCD), anorganic light emitting diode (OLED) display, an inorganic light emittingdiode (ILED) display, a micro-LED display, an active-matrix organiclight emitting diode (AMOLED) display, a transparent organic lightemitting diode (TOLED) display, some other display, or some combinationsthereof. HMD device 300 may include two eye box regions.

In some implementations, HMD device 300 may include various sensors (notshown), such as depth sensors, motion sensors, position sensors, and eyetracking sensors. Some of these sensors may use a structured lightpattern for sensing. In some implementations, HMD device 300 may includean input/output interface for communicating with a console. In someimplementations, HMD device 300 may include a virtual reality engine(not shown) that can execute applications within HMD device 300 andreceive depth information, position information, accelerationinformation, velocity information, predicted future positions, or somecombination thereof of HMD device 300 from the various sensors. In someimplementations, the information received by the virtual reality enginemay be used for producing a signal (e.g., display instructions) to theone or more display assemblies. In some implementations, HMD device 300may include locators (not shown, such as locators 126) located in fixedpositions on body 320 relative to one another and relative to areference point. Each of the locators may emit light that is detectableby an external imaging device.

FIG. 4 is a simplified block diagram of an example electronic system 400of an example near-eye display (e.g., HMD device) for implementing someof the examples disclosed herein. Electronic system 400 may be used asthe electronic system of HMD device 300 or other near-eye displaysdescribed above. In this example, electronic system 400 may include oneor more processor(s) 410 and a memory 420. Processor(s) 410 may beconfigured to execute instructions for performing operations at a numberof components, and can be, for example, a general-purpose processor ormicroprocessor suitable for implementation within a portable electronicdevice. Processor(s) 410 may be communicatively coupled with a pluralityof components within electronic system 400. To realize thiscommunicative coupling, processor(s) 410 may communicate with the otherillustrated components across a bus 440. Bus 440 may be any subsystemadapted to transfer data within electronic system 400. Bus 440 mayinclude a plurality of computer buses and additional circuitry totransfer data.

Memory 420 may be coupled to processor(s) 410. In some embodiments,memory 420 may offer both short-term and long-term storage and may bedivided into several units. Memory 420 may be volatile, such as staticrandom access memory (SRAM) and/or dynamic random access memory (DRAM)and/or non-volatile, such as read-only memory (ROM), flash memory, andthe like. Furthermore, memory 420 may include removable storage devices,such as secure digital (SD) cards. Memory 420 may provide storage ofcomputer-readable instructions, data structures, program modules, andother data for electronic system 400. In some embodiments, memory 420may be distributed into different hardware modules. A set ofinstructions and/or code might be stored on memory 420. The instructionsmight take the form of executable code that may be executable byelectronic system 400, and/or might take the form of source and/orinstallable code, which, upon compilation and/or installation onelectronic system 400 (e.g., using any of a variety of generallyavailable compilers, installation programs, compression/decompressionutilities, etc.), may take the form of executable code.

In some embodiments, memory 420 may store a plurality of applicationmodules 422 through 424, which may include any number of applications.Examples of applications may include gaming applications, conferencingapplications, video playback applications, or other suitableapplications. The applications may include a depth sensing function oreye tracking function. Application modules 422-424 may includeparticular instructions to be executed by processor(s) 410. In someembodiments, certain applications or parts of application modules422-424 may be executable by other hardware modules 480. In certainembodiments, memory 420 may additionally include secure memory, whichmay include additional security controls to prevent copying or otherunauthorized access to secure information.

In some embodiments, memory 420 may include an operating system 425loaded therein. Operating system 425 may be operable to initiate theexecution of the instructions provided by application modules 422-424and/or manage other hardware modules 480 as well as interfaces with awireless communication subsystem 430 which may include one or morewireless transceivers. Operating system 425 may be adapted to performother operations across the components of electronic system 400including threading, resource management, data storage control and othersimilar functionality.

Wireless communication subsystem 430 may include, for example, aninfrared communication device, a wireless communication device and/orchipset (such as a Bluetooth® device, an IEEE 802.11 device, a Wi-Fidevice, a WiMax device, cellular communication facilities, etc.), and/orsimilar communication interfaces. Electronic system 400 may include oneor more antennas 434 for wireless communication as part of wirelesscommunication subsystem 430 or as a separate component coupled to anyportion of the system. Depending on desired functionality, wirelesscommunication subsystem 430 may include separate transceivers tocommunicate with base transceiver stations and other wireless devicesand access points, which may include communicating with different datanetworks and/or network types, such as wireless wide-area networks(WWANs), wireless local area networks (WLANs), or wireless personal areanetworks (WPANs). A WWAN may be, for example, a WiMax (IEEE 802.16)network. A WLAN may be, for example, an IEEE 802.11x network. A WPAN maybe, for example, a Bluetooth network, an IEEE 802.15x, or some othertypes of network. The techniques described herein may also be used forany combination of WWAN, WLAN, and/or WPAN. Wireless communicationssubsystem 430 may permit data to be exchanged with a network, othercomputer systems, and/or any other devices described herein. Wirelesscommunication subsystem 430 may include a means for transmitting orreceiving data, such as identifiers of HMD devices, position data, ageographic map, a heat map, photos, or videos, using antenna(s) 434 andwireless link(s) 432. Wireless communication subsystem 430, processor(s)410, and memory 420 may together comprise at least a part of one or moreof a means for performing some functions disclosed herein.

Embodiments of electronic system 400 may also include one or moresensors 490. Sensor(s) 490 may include, for example, an image sensor, anaccelerometer, a pressure sensor, a temperature sensor, a proximitysensor, a magnetometer, a gyroscope, an inertial sensor (e.g., a modulethat combines an accelerometer and a gyroscope), an ambient lightsensor, or any other similar module operable to provide sensory outputand/or receive sensory input, such as a depth sensor or a positionsensor. For example, in some implementations, sensor(s) 490 may includeone or more inertial measurement units (IMUs) and/or one or moreposition sensors. An IMU may generate calibration data indicating anestimated position of the HMD device relative to an initial position ofthe HMD device, based on measurement signals received from one or moreof the position sensors. A position sensor may generate one or moremeasurement signals in response to motion of the HMD device. Examples ofthe position sensors may include, but are not limited to, one or moreaccelerometers, one or more gyroscopes, one or more magnetometers,another suitable type of sensor that detects motion, a type of sensorused for error correction of the IMU, or some combination thereof. Theposition sensors may be located external to the IMU, internal to theIMU, or some combination thereof. At least some sensors may use astructured light pattern for sensing.

Electronic system 400 may include a display module 460. Display module460 may be a near-eye display, and may graphically present information,such as images, videos, and various instructions, from electronic system400 to a user. Such information may be derived from one or moreapplication modules 422-424, virtual reality engine 426, one or moreother hardware modules 480, a combination thereof, or any other suitablemeans for resolving graphical content for the user (e.g., by operatingsystem 425). Display module 460 may use liquid crystal display (LCD)technology, light-emitting diode (LED) technology (including, forexample, OLED, ILED, micro-LED, AMOLED, TOLED, etc.), light emittingpolymer display (LPD) technology, or some other display technology.

Electronic system 400 may include a user input/output module 470. Userinput/output module 470 may allow a user to send action requests toelectronic system 400. An action request may be a request to perform aparticular action. For example, an action request may be to start or endan application or to perform a particular action within the application.User input/output module 470 may include one or more input devices.Example input devices may include a touchscreen, a touch pad,microphone(s), button(s), dial(s), switch(es), a keyboard, a mouse, agame controller, or any other suitable device for receiving actionrequests and communicating the received action requests to electronicsystem 400. In some embodiments, user input/output module 470 mayprovide haptic feedback to the user in accordance with instructionsreceived from electronic system 400. For example, the haptic feedbackmay be provided when an action request is received or has beenperformed.

Electronic system 400 may include a camera 450 that may be used to takephotos or videos of a user, for example, for tracking the user's eyeposition. Camera 450 may also be used to take photos or videos of theenvironment, for example, for VR, AR, or MR applications. Camera 450 mayinclude, for example, a complementary metal-oxide-semiconductor (CMOS)image sensor with a few millions or tens of millions of pixels. In someimplementations, camera 450 may include two or more cameras that may beused to capture 3-D images.

In some embodiments, electronic system 400 may include a plurality ofother hardware modules 480. Each of other hardware modules 480 may be aphysical module within electronic system 400. While each of otherhardware modules 480 may be permanently configured as a structure, someof other hardware modules 480 may be temporarily configured to performspecific functions or temporarily activated. Examples of other hardwaremodules 480 may include, for example, an audio output and/or inputmodule (e.g., a microphone or speaker), a near field communication (NFC)module, a rechargeable battery, a battery management system, awired/wireless battery charging system, etc. In some embodiments, one ormore functions of other hardware modules 480 may be implemented insoftware.

In some embodiments, memory 420 of electronic system 400 may also storea virtual reality engine 426. Virtual reality engine 426 may executeapplications within electronic system 400 and receive positioninformation, acceleration information, velocity information, predictedfuture positions, or some combination thereof of the HMD device from thevarious sensors. In some embodiments, the information received byvirtual reality engine 426 may be used for producing a signal (e.g.,display instructions) to display module 460. For example, if thereceived information indicates that the user has looked to the left,virtual reality engine 426 may generate content for the HMD device thatmirrors the user's movement in a virtual environment. Additionally,virtual reality engine 426 may perform an action within an applicationin response to an action request received from user input/output module470 and provide feedback to the user. The provided feedback may bevisual, audible, or haptic feedback. In some implementations,processor(s) 410 may include one or more GPUs that may execute virtualreality engine 426.

In various implementations, the above-described hardware and modules maybe implemented on a single device or on multiple devices that cancommunicate with one another using wired or wireless connections. Forexample, in some implementations, some components or modules, such asGPUs, virtual reality engine 426, and applications (e.g., trackingapplication), may be implemented on a console separate from thehead-mounted display device. In some implementations, one console may beconnected to or support more than one HMD.

In alternative configurations, different and/or additional componentsmay be included in electronic system 400. Similarly, functionality ofone or more of the components can be distributed among the components ina manner different from the manner described above. For example, in someembodiments, electronic system 400 may be modified to include othersystem environments, such as an AR system environment and/or an MRenvironment.

As discussed above, micro-LEDs may be used as light sources in variousparts of an artificial reality system, such as the display electronics122, the locators 126, and the eye tracking unit 130. Further,micro-LEDs may be used in various display technologies, such as heads-updisplays, television displays, smartphone displays, watch displays,wearable displays, and flexible displays. Micro-LEDs can be used incombination with a plurality of sensors in many applications such as theInternet of Things (IOT). The micro-LEDs described herein are primarilydescribed as red, blue, or green micro-LEDs; however, the micro-LEDs canbe configured to emit light having any desired wavelength, such asultraviolet or infrared light. Also, the micro-LEDs described herein areprimarily described as having parabolic mesas; however, the micro-LEDscan be configured to have any suitable mesa shape, such as planar,vertical, conical, parabolic, or combinations thereof. Further, themicro-LEDs can be configured to have any suitable base shape, such ascircular, elliptical, rectangular, triangular, or hexagonal.

FIG. 5 is a cross sectional view of an example of a micro-LED 500,according to one or more embodiments. The micro-LED 500 may include asubstrate 502, a semiconductor layer 504 shaped into a mesa 506, anactive light emitting layer 508, an outcoupling surface 510, and areflector layer 514. The outcoupling surface 510 of the micro-LED 500may be less than 20 μm in diameter. A parabolic mesa 506 may be etchedonto the LED die during wafer processing to form a quasi-collimatedlight beam emerging from the outcoupling surface 510. Alternatively, themesa 506 may have a variety of other shapes, such as planar, vertical,conical, or semi-parabolic. The micro-LED 500 can be configured to havea high light extraction efficiency, and outputs quasi-collimated lightbecause of the shape of the mesa 506. The micro-LED 500 can beconfigured to emit light having a divergence angle θ in a predeterminedrange. In various embodiments, the divergence angle θ is approximately10 degrees.

The semiconductor layer 504 is disposed on the substrate 502. Thesemiconductor layer 504 and the substrate 502 may be made of the samematerial, such as GaN. The active light emitting layer 508 is enclosedin the mesa 506. The active light emitting layer 508 may be a multiplequantum well (MQW) layer, and/or may include quantum dots, quantumwires, vertical nano-wires, and/or vertical fins. The active lightemitting layer 508 may be arranged at a focal point of the mesa 506. Themesa 506 may have a truncated top on a side opposed to the outcouplingsurface 510. The mesa 506 may have a curved or near-parabolic shape toform a reflective enclosure for light within the micro-LED 500. Thearrows 512 show how light emitted from the active light emitting layer508 is reflected off the walls of the mesa 506 toward the outcouplingsurface 510 at an angle sufficient for the light to escape the micro-LED500 (e.g., within the angle of total internal reflection). As discussedin further detail below, a reflector layer 514 may be formed on the mesa506 to improve the reflection of the light. The p- and n-contacts (notshown) may be located on the same side as the mesa 506, which isopposite the outcoupling surface 510.

The micro-LED 500 shown in FIG. 5 may be modified to improve theefficiency of the micro-LED 500. Various simulation methods may be usedto assess the efficiency. For example, FIGS. 6A and 6B show comparisonsof experimental data with simulation data for a micro-LED emitting greenlight. FIG. 6A shows that simulated operating voltage (V_(op)) data 605agrees well with experimental V_(op) data 610, and that simulated lightoutput power (LOP) data 615 agrees well with experimental LOP data 620.Similarly, FIG. 6B shows that simulated external quantum efficiency(EQE) data 635 agrees well with experimental EQE data 640. FIG. 6B alsoshows the simulated percentage of surface recombination 630. Thisillustrates that surface recombination dominates at the mesa, and shiftsthe maximum EQE to a higher current of 10-20 μA.

FIG. 7A shows additional comparisons of experimental data withsimulation data for a micro-LED emitting green light. FIG. 7A againshows the agreement between simulated LOP data 715 and experimental LOPdata 720. In addition, FIG. 7A shows that simulated wavelength data 705agrees well with experimental wavelength data 710. FIG. 7A illustratesthat there is a shift toward blue wavelengths for a green micro-LEDemitting light at 515 nm and 10 μA. FIG. 7B shows simulated internalquantum efficiency (IQE) data for a first simulation method 730 and asecond simulation method 735, along with simulated junction temperaturedata 740.

FIG. 8A shows an example of a micro-LED 800 according to one or moreembodiments. The micro-LED 800 may be similar to the micro-LED 500 shownin FIG. 5. The micro-LED 800 emits light 805 along the direction shownin FIG. 8A. FIG. 8B shows simulated LEE data for the green micro-LED 800shown in FIG. 8A. As shown in FIG. 8B, the green micro-LED 800 has anLEE of 27.17% within an emission cone having an angle of 90°, and an LEEof 1.43% within an emission cone having an angle of 10°. FIG. 8Billustrates the need to improve the LEE and to emit more light withinthe narrower emission cone.

Some embodiments may improve the LEE and the beam profile of a micro-LEDby modifying the mesa shape of the micro-LED. FIGS. 9A-9C show variousexamples of green micro-LEDs having different mesa shapes. The height,width, and/or curvature of the micro-LED may be adjusted to optimize theLEE and the beam profile.

As shown in FIG. 9A, a mesa including an n-side semiconductor 905 and ap-side semiconductor 910 may be arranged on a substrate 915, and ap-contact (not shown) may be provided at the top of the p-sidesemiconductor 910. An active light emitting layer 907, such as an MQWlayer, may be positioned at the interface between the n-sidesemiconductor 905 and the p-side semiconductor 910. The mesa has asemi-parabolic shape with a height of 1.3 μm and a bottom diameter of3.5 μm. The micro-LED shown in FIG. 9A has an LEE of 21.17% within anemission cone having an angle of 90°, and an LEE of 0.91% within anemission cone having an angle of 10°.

As shown in FIG. 9B, a mesa including an n-side semiconductor 920 and ap-side semiconductor 925 may be arranged on a substrate 930, and ap-contact (not shown) may be provided at the top of the p-sidesemiconductor 925. An active light emitting layer 927, such as an MQWlayer, may be positioned at the interface between the n-sidesemiconductor 920 and the p-side semiconductor 925. The mesa has aparabolic shape with a height of 1.3 μm and a bottom diameter of 3.0 μm.The micro-LED shown in FIG. 9B has an LEE of 27.17% within an emissioncone having an angle of 90°, and an LEE of 1.43% within an emission conehaving an angle of 10°.

As shown in FIG. 9C, a mesa including an n-side semiconductor 935 and ap-side semiconductor 940 may be arranged on a substrate 945, and ap-contact (not shown) may be provided at the top of the p-sidesemiconductor 940. Alternatively, the mesa may be arranged on a thincurrent spreading layer having a typical thickness between 2 and 8 μm,in which case the substrate has been removed. The mesa has a parabolicshape with a height of 1.5 μm and a bottom diameter of 3.0 μm. Themicro-LED shown in FIG. 9C has an improved LEE of 31.21% within anemission cone having an angle of 90°, and an LEE of 1.62% within anemission cone having an angle of 10°. A comparison of FIGS. 9A-9Cillustrates that the LEE and beam profile of a micro-LED can be improvedby using a mesa with a parabolic shape instead of a semi-parabolicshape, and by increasing the height of the mesa. Inductively coupledplasma (ICP) etching may be used as a high-accuracy method to form thedesired mesa shape.

Alternatively or in addition, some embodiments may improve the LEE andthe beam profile of a micro-LED by providing a reflector layer on anouter surface of the mesa of the micro-LED. FIGS. 10A-10C show variousexamples of green micro-LEDs having different reflector layers. Forexample, the reflector layer may include different sub-layers havingdifferent materials and different thicknesses. Also, different reflectorlayers may be provided for the mesa and the p-contact. Alternatively,the reflector layer may be used with no other layers by using the largedifference in refractive index between the semiconductor material andair.

As shown in FIG. 10A, a mesa including an n-side semiconductor 1001 anda p-side semiconductor 1004 may be arranged on a substrate 1002, and ap-contact 1003 may be provided at the top of the p-side semiconductor1004. A first reflector layer that is formed on an outer surface of themesa may include an SiN layer 1005 and a layer 1006 including, in orderfrom the SiN layer 1005, Ti and Au. The SiN layer 1005 may have athickness between 100 nm and 400 nm, such as 200 nm. The Ti layer mayhave a thickness between 1 nm and 30 nm, such as 20 nm. The Au layer mayhave a thickness between 100 nm and 500 nm, such as 300 nm. Thep-contact 1003 that is formed on an outer surface of the p-semiconductor1004 may include in order from the p-side semiconductor 1004, a Ni layerand an Au layer. The Ni layer may have a thickness between 5 nm and 30nm, such as 20 nm. The Au layer may have a thickness between 20 nm and330 nm, such as 300 nm. The micro-LED shown in FIG. 10A has an LEE of31.21% within an emission cone having an angle of 90°, and an LEE of1.62% within an emission cone having an angle of 10°.

As shown in FIG. 10B, a mesa including an n-side semiconductor 1011 anda p-side semiconductor 1014 may be arranged on a substrate 1012, and ap-contact 1013 may be provided at the top of the p-side semiconductor1014. A first reflector layer that is formed on an outer surface of themesa may include an SiN layer 1015 and a layer 1016 including, in orderfrom the SiN layer 1015, Ti and Au. The SiN layer 1015 may have athickness between 100 nm and 400 nm, such as 200 nm. The Ti layer mayhave a thickness between 1 nm and 30 nm, such as 20 nm. The Au layer mayhave a thickness between 100 nm and 500 nm, such as 300 nm. Thep-contact 1013 that is formed on an outer surface of the p-sidesemiconductor 1014 may include, in order from the p-side semiconductor1014, an Ag layer, a Pt layer, and an Au layer. The Ag layer may have athickness between 90 nm and 300 nm, such as 100 nm. The Pt layer mayhave a thickness between 20 nm and 50 nm, such as 25 nm. The Au layermay have a thickness between 100 nm and 500 nm, such as 300 nm. Themicro-LED shown in FIG. 10B has an LEE of 35.2% within an emission conehaving an angle of 90°, and an LEE of 1.9% within an emission conehaving an angle of 10°.

As shown in FIG. 10C, a mesa including an n-side semiconductor 1021 anda p-side semiconductor 1024 may be arranged on a substrate 1022, and ap-contact 1023 may be provided at the top of the p-side semiconductor1024. A first reflector layer that is formed on an outer surface of themesa may include an SiN layer 1025 and a layer 1026 including, in orderfrom the SiN layer 1025, Ag, Pt, and Au. The SiN layer 1025 may have areduced thickness between 40 nm and 100 nm, such as 75 nm. The Ag layermay have a thickness between 60 nm and 150 nm, such as 100 nm. The Ptlayer may have a thickness between 20 nm and 30 nm, such as 25 nm. TheAu layer may have a thickness between 100 nm and 200 nm, such as 125 nm.The p-contact 1023 that is formed on an outer surface of the p-sidesemiconductor 1024 may include, in order from the p-side semiconductor1024, an Ag layer, a Pt layer, and an Au layer. The Ag layer may have athickness between 60 nm and 150 nm, such as 100 nm. The Pt layer mayhave a thickness between 20 nm and 30 nm, such as 25 nm. The Au layermay have a thickness between 110 nm and 140 nm, such as 125 nm. Themicro-LED shown in FIG. 10C has an LEE of 50.1% within an emission conehaving an angle of 90°, and an LEE of 2.65% within an emission conehaving an angle of 10°. The thin reflector design shown in FIG. 10C maybe optimized for a high reflectivity with thin layer stacks and a veryclose pitch (such as less than 5 μm) of many micro-LEDs in one- ortwo-dimensional arrays, such as for super resolution 1-4K displayapplications.

Although specific materials having specific thicknesses are describedabove, the reflector layers may include any suitable materials havingany suitable thicknesses. The materials and their thicknesses may bechosen based on the desired emission wavelength and the semiconductormaterial. Further, the materials and their thicknesses may be chosen inorder to achieve specific outcomes. For example, with reference to themicro-LED shown in FIG. 10C, the SiN layer 1025 may be configured toserve as a dielectric passivation layer that prevents shortage of thep/n junction and avoids resonance, such as resonant absorption, withinthe optical cavity. The SiN may be replaced with any suitable dielectricmaterial, such as SiO₂, HfO, or AlO. The Ag layer within layer 1026 maybe configured to serve as an adhesion layer that also providesreflectivity. The Ag should not be replaced with an adhesion metalhaving a high light absorption, such as Ti, due to the high lightabsorption even for small layer thickness of 10-20 nm. The Pt layerwithin layer 1026 may be configured to serve as a diffusion barrierlayer that reduces interdiffusion between various layers. The Pt layermay also serve as a protective layer for the Ag layer and to avoidoxidation. The Au layer within layer 1026 may be configured to serve asan additional coating and protection layer.

Further, with reference to the micro-LED shown in FIG. 10C, materialsand thicknesses of the p-contact 1023 may be chosen based on the desiredemission wavelength and the semiconductor material. Further, thematerials and their thicknesses may be chosen in order to achievespecific outcomes. For example, the Ag layer may be replaced by an Allayer for green or blue micro-LEDs, and the Ag layer may be replaced byan Au layer for red or IR micro-LEDs. In addition, the Pt layer may bereplaced by another diffusion barrier layer, such as a Pd, WTi, or WNlayer. Further, the Au layer may be replaced by an Al layer.

FIGS. 11A and 11B show reflection coefficients for a typical reflectordesign and an optimized reflector design, respectively, of greenmicro-LEDs. For example, FIG. 11A shows the transverse electric (TE) andtransverse magnetic (TM) coefficients as a function of angle for thegreen micro-LED shown in FIG. 10B. Similarly, FIG. 11B shows the TE andTM coefficients as a function of angle for the green micro-LED shown inFIG. 10C. As shown in FIGS. 11A and 11B, the reflective layers in thegreen micro-LED shown in FIG. 10C achieve a significantly higherreflection, which leads to a higher LEE.

Some embodiments may improve the LEE and the beam profile of a micro-LEDby incorporating an anti-reflection coating on the outcoupling surfaceof the micro-LED, providing an index-matched material between theoutcoupling surface of the micro-LED and a downstream optical element,and/or providing secondary optics on the outcoupling surface of themicro-LED. FIGS. 12A-12C show various examples of green micro-LEDshaving different components to optimize the LEE and the beam profile.

As shown in FIG. 12A, a mesa including an n-side semiconductor 1201 anda p-side semiconductor 1204 may be arranged on a substrate 1202, and ap-contact 1215 may be provided at the top of the p-side semiconductor1204. Alternatively, the mesa may be arranged on an n-current spreadinglayer without a substrate. A reflector layer that is formed on an outersurface of the mesa may include a layer 1205 and a layer 1206. Anoptical element 1211 may receive light 1210 from an outcoupling surface1208 of the substrate 1202. An anti-reflection coating 1209 may bearranged on the outcoupling surface 1208. The micro-LED shown in FIG.12A has an LEE of 52.2% within an emission cone having an angle of 90°,and an LEE of 2.96% within an emission cone having an angle of 10°. Themicro-LED shown in FIG. 12A uses the micro-LED shown in FIG. 10C, butadds the anti-reflection coating 1209 and provides light to the opticalelement 1211.

As shown in FIG. 12B, a mesa including an n-side semiconductor 1221 anda p-side semiconductor 1224 may be arranged on an n-current spreadingsubstrate 1222, and a p-contact 1235 may be provided at the top of thep-side semiconductor 1224. A reflector layer that is formed on an outersurface of the mesa may include a layer 1225 and a layer 1226. Anoptical element 1231 may receive light 1230 from an outcoupling surface1228 of the substrate 1222. An index-matched material 1229 may bearranged between the outcoupling surface 1228 and the optical element1231. An index of refraction of the index-matched material 1229 may begreater than 1, and/or greater than or equal to an index of refractionof the optical element 1231. For example, if the optical element 1231has an index of refraction of 1.5, the index-matched material 1229 mayhave an index of refraction between 1.5 and 1.7. In other examples, theindex-matched material 1229 may have an index of refraction up to 2.2.The index-matched material 1229 may be made of any suitable material,such as silicone. The micro-LED shown in FIG. 12A has an LEE of 81.1%within an emission cone having an angle of 90°, and an LEE of 5.94%within an emission cone having an angle of 10°. The micro-LED shown inFIG. 12B uses the micro-LED shown in FIG. 10C, but adds theindex-matched material 1229 and provides light to the optical element1231.

As shown in FIG. 12C, a mesa including an n-side semiconductor 1241 anda p-side semiconductor 1244 may be arranged on an n-current spreadingsubstrate 1242, and a p-contact 1255 may be provided at the top of thep-side semiconductor 1244. A reflector layer that is formed on an outersurface of the mesa may include a layer 1245 and a layer 1246. Anoptical element 1251 may receive light 1250 from an outcoupling surface1248 of the substrate 1242. Secondary optics 1252 may be arrangedbetween the outcoupling surface 1248 and the optical element 1251. Forexample, the secondary optics 1252 may be a lens. The lens may be aseparate optical component, or may be etched into the outcouplingsurface 1248. The lens may have a focal point at an active emittinglayer of the micro-LED. FIG. 12C shows a measured beam profile 1254 anda simulated beam profile 1253. The micro-LED shown in FIG. 12C uses themicro-LED shown in FIG. 10C, but adds the secondary optics 1252 andprovides light to the optical element 1251.

FIGS. 13A-13C show various examples of red micro-LEDs having differentcomponents to optimize the LEE and the beam profile. As shown in FIG.13A, a mesa including an n-side semiconductor 1301 and a p-sidesemiconductor 1304 may be arranged on a substrate 1302, and a p-contact1315 may be provided at the top of the p-side semiconductor 1304. Areflector layer that is formed on an outer surface of the mesa mayinclude a layer 1305 and a layer 1306. An optical element 1311 mayreceive light 1310 from an outcoupling surface 1308 of the substrate1302. An anti-reflection coating 1309 may be arranged on the outcouplingsurface 1308. The micro-LED shown in FIG. 13A has an LEE of 30.5% withinan emission cone having an angle of 90°, and an LEE of 1.5% within anemission cone having an angle of 10°. The optical element 1311 may havea corresponding acceptance angle of 10°.

As shown in FIG. 13B, a mesa including an n-side semiconductor 1321 anda p-side semiconductor 1324 may be arranged on a substrate 1322, and ap-contact 1335 may be provided at the top of the p-side semiconductor1324. A reflector layer that is formed on an outer surface of the mesamay include a layer 1325 and a layer 1326. An optical element 1331 mayreceive light 1330 from an outcoupling surface 1328 of the substrate1322. Secondary optics 1332 may be arranged between the outcouplingsurface 1328 and the optical element 1331. For example, the secondaryoptics 1332 may be a lens. The lens may be a separate optical component,or may be etched into the outcoupling surface 1328. The lens may have afocal point at an active emitting layer of the micro-LED. In the exampleshown in FIG. 13B, the lens is a spherical lens whose diameter isapproximately equal to the diameter of the outcoupling surface 1328. Themicro-LED shown in FIG. 13B has an LEE of 61.0% within an emission conehaving an angle of 90°, and an LEE of 2.2% within an emission conehaving an angle of 10°. The optical element 1331 may have acorresponding acceptance angle of 10°.

As shown in FIG. 13C, a mesa including an n-side semiconductor 1341 anda p-side semiconductor 1344 may be arranged on a substrate 1342, and ap-contact 1355 may be provided at the top of the p-side semiconductor1344. A reflector layer that is formed on an outer surface of the mesamay include a layer 1345 and a layer 1346. An optical element 1351 mayreceive light 1350 from an outcoupling surface 1348 of the substrate1342. Secondary optics 1352 may be arranged between the outcouplingsurface 1348 and the optical element 1351. For example, the secondaryoptics 1352 may be a lens. The lens may be a separate optical component,such as a resist including a polymer such as Poly(methyl acrylate) (PMA)or glass, or may be etched into the outcoupling surface 1348. The lensmay have a focal point at an active emitting layer of the micro-LED. Inthe example shown in FIG. 13C, the lens is a spherical lens whosediameter is greater than to the diameter of the outcoupling surface1328. FIG. 12C shows a measured beam profile 1354 and a simulated beamprofile 1353. The micro-LED shown in FIG. 13C has an LEE of 76.2% withinan emission cone having an angle of 90°, and an LEE of 3.4% within anemission cone having an angle of 10°. The optical element 1531 may havea corresponding acceptance angle of 10°.

FIGS. 14A and 14B show the effects of incorporating an index-matchedmaterial between the outcoupling surface and the optical element for agreen micro-LED. FIG. 14A shows the reflection coefficient at theoutcoupling surface to air (n=1) for a green micro-LED without theindex-matched material, while FIG. 14B shows the reflection coefficientat the outcoupling surface for a green micro-LED with the index-matchedmaterial (for example, n=1.5 for typical silicone materials). The arrow1405 in FIG. 14A indicates an increase in the angle of the emissioncone, while the arrow 1410 in FIG. 14B indicates a decrease in thereflection coefficient at the outcoupling surface. Because thereflectivity decreases at the outcoupling surface, and the totalinternal reflection (TIR) angle shifts to higher wavelengths, themicro-LED has improved light out-coupling and improved light emissioninto a narrow cone. Accordingly, incorporating the index-matchedmaterial improves the light out-coupling from the chip, and directs morelight into the emission cone having an angle of 10°.

The index-matched material may be incorporated into micro-LEDs invarious applications. For example, a high coupling efficiency may beachieved by butt-coupling the index-matched material to an opticalelement that is a waveguide that may be used in display and/orprojection systems. The waveguide may be an ultra-thin and/or flexiblewaveguide, and may include a volume Bragg grating (VBG) or a surfacerelief grating (SRG) as passive beam shaping features. The index-matchedmaterial may also be incorporated into micro-LEDs that are used inone-dimensional and/or two-dimensional displays, including displays thatuse scanning, microelectromechanical systems (MEMS), gratings, liquidcrystal displays (LCDs), and/or liquid crystal on silicon (LCOS)displays.

FIGS. 15A-15C show various examples of red micro-LEDs having differentsecondary optics to optimize the LEE and the beam profile. As shown inFIG. 15A, a mesa including an n-side semiconductor 1502 and a p-sidesemiconductor 1501 may be arranged on a substrate 1503. The micro-LEDshown in FIG. 15A does not include any secondary optics at theoutcoupling surface 1507 of the substrate 1503. FIG. 15A shows themeasured beam profile 1504 of the micro-LED.

As shown in FIG. 15B, a mesa including an n-side semiconductor 1512 anda p-side semiconductor 1511 may be arranged on a substrate 1513. Themicro-LED shown in FIG. 15B includes secondary optics 1516 at theoutcoupling surface 1517 of the substrate 1503. In this example, thesecondary optics 1516 is a spherical lens. FIG. 15A shows the measuredbeam profile 1515 and the simulated beam profile 1514 of the micro-LED.

As shown in FIG. 15C, a mesa including an n-side semiconductor 1522 anda p-side semiconductor 1521 may be arranged on a substrate 1523. Themicro-LED shown in FIG. 15C includes secondary optics 1526 at theoutcoupling surface 1527 of the substrate 1523. In this example, thesecondary optics 1526 is a Fresnel lens. FIG. 15C shows the measuredbeam profile 1525 and the simulated beam profile 1524 of the micro-LED.As shown in FIG. 15C, the Fresnel lens shown in this example having adifferent focal point in the center and the outer areas causes morelight to be emitted into an emission cone having a narrower angle.

FIGS. 16A and 16B show an example of a green micro-LED having secondaryoptics to optimize the LEE and the beam profile. As shown in FIG. 16A, amesa including an n-side semiconductor 1602 and a p-side semiconductor1601 may be arranged on a substrate including a first layer 1603 and asecond layer 1604. The first layer 1603 and the second layer 1604 may bemade of the same material, such as 60% AlGaAs. The micro-LED shown inFIG. 16A includes secondary optics 1605 at the outcoupling surface 1607of the substrate. In this example, the secondary optics 1605 is aspherical lens. The focal point of the spherical lens may be at theactive light emitting layer of the micro-LED. Further, ananti-reflection coating may be arranged on an outer surface of thespherical lens, in order to reduce any Fresnel losses. In this example,the mesa has a height of 1.5 μm and the spherical lens has a height of0.5 μm. FIG. 16B shows the intensity of the beam profile of lightemitted by the micro-LED shown in FIG. 16A. The micro-LED shown in FIG.13C has an LEE of 76.2% within an emission cone having an angle of 90°,and an LEE of 3.4% within an emission cone having an angle of 10°. If asmaller spherical lens is used, such as a spherical lens with a heightof 0.3 μm, the LEE decreases to 61.0% within an emission cone having anangle of 90°, and the LEE decreases to 2.2% within an emission conehaving an angle of 10°.

FIGS. 17A and 17B show examples of red and green micro-LEDs havingsecondary optics to optimize the LEE and the beam profile. As shown inFIG. 17A, a mesa including an n-side semiconductor 1702 and a p-sidesemiconductor 1701 may be arranged on a substrate 1703. The redmicro-LED shown in FIG. 17A includes secondary optics 1704 at theoutcoupling surface 1710 of the substrate 1703. In this example, thesecondary optics 1704 is a spherical lens with partial openings. Thefocal point of the lens may be at the active light emitting layer of themicro-LED. Light 1707 emitted from the active light emitting layer formsa beam profile 1705, and may be shaped to approximate a top-hat beamprofile 1706. As shown in FIG. 17A, the light 1707 is reflected at themesa facet and is incident on the outcoupling surface 1710 within anarrow emission cone.

As shown in FIG. 17B, a mesa including an n-side semiconductor 1712 anda p-side semiconductor 1711 may be arranged on a substrate 1713. Thegreen micro-LED shown in FIG. 17B includes secondary optics 1714 at theoutcoupling surface 1720 of the substrate 1713. In this example, thesecondary optics 1714 is a spherical lens with partial openings. Thefocal point of the lens may be at the active light emitting layer of themicro-LED. Light 1717 emitted from the active light emitting layer formsa Lambertian beam profile 1715 without lens (HWHM=60°), which is widerthan the beam profile 1706 (HWHM<60°) shown in FIG. 17A. The beamprofile of light 1717 can be improved with a lens as shown in FIG. 17Band reproduced in FIG. 17B as beam profile 1718 similar to 1705, whichboth approximate a top-hat beam profile 1716. As shown in FIG. 17B, thelight 1717 includes forward travelling and backward reflected light thatis incident on the outcoupling surface 1720 within a narrow emissioncone 1718. Without additional secondary optics, the beam profile 1715 ofthe group of green rays within the micro-LED shown in FIG. 17B has amore Lambertian shape than the narrower beam profile 1705 of the groupof red rays reflected at the mesa facet within the micro-LED having thesame structure shown in FIG. 17A.

FIGS. 18A-18H show examples of a red micro-LED having secondary opticsto optimize the LEE and the beam profile. As shown in FIGS. 18A-18C, amesa including an n-side semiconductor 1802 and a p-side semiconductor1801 may be arranged on a substrate 1803. Alternatively, the mesa may bearranged on a current spreading layer without a substrate. The redmicro-LED shown in FIG. 18C includes secondary optics 1810 at theoutcoupling surface 1812 of the substrate 1803. In this example, thesecondary optics 1810 is a donut-shaped lens with a maximum thicknesswhere light 1809 exits the outcoupling surface 1812, and a minimumthickness at a center of the lens. The focal point of the lens may be atthe active light emitting layer of the micro-LED. The light 1809 mayhave an intensity distribution 1820 and a beam profile 1821 as shown inFIG. 18D. FIGS. 18E-18H show additional examples of the intensitydistribution and beam profile without the lens. FIGS. 18D and 18H showthe far field and FIG. 18G shows the near field. Although FIGS. 18A-18Hshow a red micro-LED having a parabolic mesa 1802, the mesa 1802 mayalso have a planar, vertical, conical, or semi-parabolic shape.

FIGS. 19A and 19B show examples of red and green micro-LEDs havingsecondary optics to optimize the LEE and the beam profile. As shown inFIG. 19A, a mesa including an n-side semiconductor 1902 and a p-sidesemiconductor 1901 may be arranged on a substrate 1903. The redmicro-LED shown in FIG. 19A includes secondary optics 1904 and 1908 atthe outcoupling surface 1909 of the substrate 1903. In this example, thesecondary optics 1904 and 1908 include various lenses. The focal pointof the lenses may be at the active light emitting layer of themicro-LED. Light 1907 emitted from the active light emitting layer formsa beam profile 1905, and may be shaped to approximate a top-hat beamprofile 1906 with a HWHM between ±10° and ±30°.

As shown in FIG. 19B, a mesa including an n-side semiconductor 1912 anda p-side semiconductor 1911 may be arranged on a substrate 1913. Thegreen micro-LED shown in FIG. 19B includes secondary optics 1914 and1918 at the outcoupling surface 1919 of the substrate 1913. In thisexample, the secondary optics 1914 and 1918 include various lenses. Thefocal point of the lens may be at the active light emitting layer of themicro-LED. Light 1917 emitted from the active light emitting layer formsa beam profile 1920 without lens, which is wider than a beam profile1916 with lens that approximates a top-hat beam profile 1916. The beamprofile 1920 of the group of green rays within the micro-LED shown inFIG. 19B has a more Lambertian shape than the narrower beam profile 1905of the group of red rays reflected at the mesa facet within themicro-LED having the same structure shown in FIG. 19A. A different lensprofile and a different focal point are used for the red ray group andthe green ray group. The beam profile 1920 of the green ray group in themicro-LED shown in FIG. 19B with a more Lambertian shape is focusedtowards the center by a larger spherical lens 1918 to get closer to thetarget top-hat beam profile 1916 of the micro-LED shown in FIG. 19B. Thegroup of red rays is collimated by a donut like lens 1904 having adifferent shape and focal point to get closer to the target top-hat beamprofile 1906 of the micro-LED shown in FIG. 19A. Overall the LEE ofmicro-LED structures with a lens on the outcoupling surface is higherthan the LEE of micro-LED structures without a lens on the outcouplingsurface.

In some embodiments, it may be desirable to produce light that ispolarized. FIGS. 20A and 20B show an example of a green micro-LED thatemits polarized light. As shown in FIG. 20B, a mesa including an n-sidesemiconductor 2002 and a p-side semiconductor 2001 may be arranged on asubstrate 2003. A linear array grating 2004 may be formed on anoutcoupling surface 2005 of the substrate 2003. An example of the lineararray grating 2004 is shown in FIG. 20A. The linear array grating 2004transmits TE light at a different percentage than TM light. The lineararray grating 2004 may be etched into the outcoupling surface 2005 orgrown as a separate component on the outcoupling surface 2005.

FIGS. 21A and 21B show the reflection coefficient as a function of anglefor various micro-LED configurations. As shown in FIGS. 21A and 21B, theTE/TM-light reflection ratio is approximately 45° at a parabolic mesafacet. The reflector layer design may be optimized for very differentreflectivity of light for the TE and TM modes (at around 45° atparabolic mesa facet) inside the micro-LED. Alternatively, the mesa mayalso have a planar, vertical, conical, or semi-parabolic shape. In otherembodiments, the mesa may have a non-rotationally symmetric shape, suchas a bathtub-like shape. FIG. 22A shows an example of a micro-LED with amesa having a non-rotationally symmetric shape. FIG. 22B shows anexample of a mesa having a planar shape, in which light may be generatedaway from the chip edge. FIG. 22C shows an example of a mesa having aconical shape, in which the angle may be 45°±5° for a high LEE via thebottom surface, and may vary slightly for different materials andwavelengths. The micro-LED may also have various base forms, such ascircular, elliptical, hexagonal, rectangular, and/or triangular. FIG.22D shows an example of a base shape that may be used in a micro-LED.

In some embodiments, the efficiency of a micro-LED may be improved byreducing surface recombination at the mesa facet. Due to the smalldimensions of the micro-LED, edge effects are significant, because theedges of the mesa are close together. Dangling bonds at the surfacecause non-radiative recombination of electrons and holes, such that only10-20% of the current reaches the active light emitting layer foremission in a red micro-LED having a 1-2 μm diameter MQW.

Current density (J)-reduction may reduce or eliminate surfacerecombination at the mesa facet. J-reduction can be achieved by variousmethods, such as ion implantation or quantum mixing. The crystal may bechanged locally such that carriers are unable to diffuse to the surfaceof the mesa. Single Quantum Well (SQW) or Double Quantum Well (DQW)designs may be used for planar, vertical, conical, or parabolic blue orgreen micro-LEDs at low current densities. Fewer quantum wells withhigher carrier concentrations may lead to less lateral carrier spreadinginside the active light emitting layer.

As discussed in further detail below, surface recombination may bereduced by various methods. FIGS. 23A-23C show the EQE and the surfacerecombination for different carrier lifetimes in a green micro-LED. Forexample, FIG. 23A shows the simulated EQE 2305 and the measured EQE 2310for a micro-LED having a carrier lifetime of 200 ns. FIG. 23A also showsthe simulated surface recombination 2315. As shown at 2320, themicro-LED has a maximum EQE of 4.6% at a current of 0.2 μA. Similarly,FIG. 23B shows the simulated EQE 2325 and the measured EQE 2330 for amicro-LED having a non-radiative (A*N) carrier lifetime of 40 ns. FIG.23B also shows the simulated surface recombination 2335. As shown at2340, the micro-LED has a maximum EQE of 4.2% at a current of 0.5 μA.Likewise, FIG. 23C shows the simulated EQE 2345 and the measured EQE2350 for a micro-LED having a non-radiative carrier lifetime of 4 ns.FIG. 23C also shows the simulated surface recombination 2355. As shownat 2360, the micro-LED has a maximum EQE of 3.7% at a current of 1.0 μA.

FIGS. 24A and 24B show an example of a method of reducing the surfacerecombination by reducing the surface states at the mesa facet. As shownin FIG. 24A, a p-contact 2401 may be provided at the top of a mesa 2402,and current 2403 may flow through an active emitting layer, such as amultiple quantum well (MQW). ICP etching may be used to reduce thesurface states by smoothing the surface of the mesa facet. Alternativelyor in addition, the surface of the mesa facet may be treated by variousmethods before deposition, such as insitu thermal cleaning, insitusurface cleaning by low energy ions such as electron cyclotron resonance(ECR) ions, or H₂-clean in vacuum such as molecular beam epitaxy (MBE).Further, the deposition of a dielectric passivation layer on the surfaceof the mesa facet may be optimized. For example, a crystalline layersuch as AlN may be deposited by MBE, and/or an SiN layer or an SiO₂layer may be deposited by inductively coupled plasma-enhanced chemicalvapor deposition (ICPECVD) using a dense plasma with low energy or byatomic layer deposition (ALD). FIG. 24B shows that a low surfacerecombination velocity (SRV) much less than 10{circumflex over ( )}4cm/s may be achieved for various micro-LEDs.

FIGS. 25A-25C show a comparison of the EQE and surface recombinationlosses for untreated green, blue, and red micro-LEDs. For example, FIG.25A shows the simulated EQE 2310 and the measured EQE 2315 for a greenmicro-LED. FIG. 25A also shows the simulated surface recombination 2505.The green micro-LED has approximately 30% surface recombination lossesat the maximum EQE due to in-potential fluctuations. Similarly, FIG. 23Bshows the simulated EQE 2530 and the measured EQE 2535 for a bluemicro-LED. FIG. 23B also shows the simulated surface recombination 2525.The blue micro-LED has the highest EQE, but with 50% surfacerecombination losses. The blue micro-LED has less in-potentialfluctuations than the green micro-LED. Likewise, FIG. 23C shows thesimulated EQE 2550 and the measured EQE 2555 for a red micro-LED. FIG.23C also shows the simulated surface recombination 2545. The redmicro-LED has the lowest EQE with greater than 80% surface recombinationlosses.

FIGS. 26A-26C show a comparison of the EQE and surface recombinationlosses for treated green, blue, and red micro-LEDs. The surfacerecombination losses were reduced by reducing the lateral carrierdiffusion and the surface recombination velocity at the mesa facet, asdiscussed above. For example, FIG. 26A shows the simulated EQE 2605 andthe measured EQE 2610 for a green micro-LED. FIG. 26A also shows thatthe simulated surface recombination and lateral carrier diffusion 2615is close to zero. The green micro-LED has a maximum EQE of approximately10% and minimal surface recombination losses. Similarly, FIG. 26B showsthe simulated EQE 2630 and the measured EQE 2625 for a blue micro-LED.FIG. 26B also shows that the simulated surface recombination 2635 isclose to zero. The blue micro-LED has a maximum EQE of approximately 31%and minimal surface recombination losses. Likewise, FIG. 26C shows thesimulated EQE 2650 and the measured EQE 2645 for a red micro-LED. FIG.26C also shows that the simulated surface recombination 2655 is close tozero. The red micro-LED has a maximum EQE of approximately 33% andminimal surface recombination losses. A comparison of FIGS. 25A-25C withFIGS. 26A-26C indicates that the treatment reduces the surfacerecombination and increases the EQE for each micro-LED.

FIGS. 27A-27C show an example of a method of reducing the surfacerecombination by reducing the lateral electron-hole (e-h) diffusion tothe mesa facet inside the active light emitting area. This may modifythe strain at the mesa facet, such that in-plane tensile strainincreases the band gap of the semiconductor material.

As shown in FIG. 27A, a mesa may include an n-side semiconductor 2702and a p-side semiconductor 2701. A resist 2704 may be used to mask acentral portion of the mesa, and various techniques may be used toreduce the lateral e-h diffusion. For example, ion implantation orquantum well intermixing may be applied along arrows 2703. Planar ionimplantation may be applied before or after ICP-etching of the mesa2702. Off-angle ion implantation may be applied to reduce the amount ofdefect generation in the active light emitting layer. FIG. 27B shows theseparation of the Ga and In atoms 2710 before quantum well intermixing2712, and the change in the distribution of the Ga and In atoms 2711after quantum well intermixing 2712. FIG. 27B also includes a graphshowing the photoluminescence intensity as a function of energy forvarious materials. As shown in FIG. 27B, the photoluminescence intensity2715 for an as-grown sample peaks at 2.74 eV, while thephotoluminescence intensity 2716 for a SiO₂ capped region peaks at 2.74eV, and the photoluminescence intensity 2717 for an Mo:SiO₂ cappedregion peaks at 2.82 eV. This shows that different capping leads tolateral different intermixing of atoms in the crystal structure. FIG.27C shows a comparison between the peak energy as a function of distancefor a non-intermixed region 2720 of SiO₂ and an intermixed region 2721of Mo:SiO₂. As shown in FIG. 27C, the regions have conduction bandsE_(c) and valence bands E_(v) with different shapes and levels. Thisshows that the region with intermixing has a higher peak energy and nolight absorption. The higher energy at mesa edge may act as a barrierfor lateral carrier diffusion.

FIGS. 28A and 28B show an example of a method of reducing the lateralcurrent spreading by performing lateral ion implantation for a definedcurrent aperture. FIG. 28A shows a micro-LED having a high contactresistance and a high operating voltage V_(f). This is caused by thesmall area of the p-contact 2805. In contrast, FIG. 28B shows ap-contact 2825 having a large area, between 20% and 1000% greater thanthe p-contact 2805. The lateral ion implantation limits the active lightemitting layer 2845 to a small area, such as a diameter between 0.5 and4 μm. The vertical droplet-like broadening of the vertical implantationprofile may maintain electrical conductivity of the top p-layer having alarger area than the active light emitting layer 2845 for lower contactresistance with p-metal. A comparison of FIGS. 28A and 28B shows thatthe lateral current spreading is limited by the performance of lateralion implantation.

The surface recombination may also be reduced during epitaxy of the mesashape. For example, the lateral e-h diffusion may be reduced byincorporating quantum dots into the quantum well for lateral carrierconfinement. This may also result in a shorter carrier lifetime.Further, using a lateral quantum barrier may provide strain release atthe mesa facet and increase the bandgap for tensile trained InGaPquantum wells. Instead of quantum dots, small micron-size quantum wires,fin-wall like structures, and/or nano-wires can also be used.

In some embodiments, the wall-plug efficiency (WPE) of a micro-LED maybe increased by reducing the operating voltage V_(f) of the micro-LED.For example, ion implantation may be used to increase the p-GaN contactarea with a smaller current aperture. A droplet implantation design inthe vertical direction may increase the p-contact area for lower contactresistance, but define a smaller current aperture above and in theactive light emitting layer. To reduce the defect generation caused byion implantation, a small angle to the surface and crystal planesreduces channeling effects. In addition, thermal annealing after ionimplantation reduces crystal damage and non-radiative absorption lossesin the active light emitting layer. As an alternative to ionimplantation, etching and regrowth may be performed.

Although the micro-LEDs disclosed above are generally described ashaving a p-side semiconductor above the active light emitting layer andan n-side semiconductor below the active light emitting layer, thepolarity could be reversed, such that an n-side semiconductor is formedabove the active light emitting layer and a p-side semiconductor isformed below the active light emitting layer. Further, a tunnel junctionmay be implemented in the epilayer, in order to reduce the contact andseries resistance in the micro-LEDs.

The methods, systems, and devices discussed above are examples. Variousembodiments may omit, substitute, or add various procedures orcomponents as appropriate. For instance, in alternative configurations,the methods described may be performed in an order different from thatdescribed, and/or various stages may be added, omitted, and/or combined.Also, features described with respect to certain embodiments may becombined in various other embodiments. Different aspects and elements ofthe embodiments may be combined in a similar manner. Also, technologyevolves and, thus, many of the elements are examples that do not limitthe scope of the disclosure to those specific examples.

Specific details are given in the description to provide a thoroughunderstanding of the embodiments. However, embodiments may be practicedwithout these specific details. For example, well-known circuits,processes, systems, structures, and techniques have been shown withoutunnecessary detail in order to avoid obscuring the embodiments. Thisdescription provides example embodiments only, and is not intended tolimit the scope, applicability, or configuration of the invention.Rather, the preceding description of the embodiments will provide thoseskilled in the art with an enabling description for implementing variousembodiments. Various changes may be made in the function and arrangementof elements without departing from the spirit and scope of the presentdisclosure.

Also, some embodiments were described as processes depicted as flowdiagrams or block diagrams. Although each may describe the operations asa sequential process, many of the operations may be performed inparallel or concurrently. In addition, the order of the operations maybe rearranged. A process may have additional steps not included in thefigure. Furthermore, embodiments of the methods may be implemented byhardware, software, firmware, middleware, microcode, hardwaredescription languages, or any combination thereof. When implemented insoftware, firmware, middleware, or microcode, the program code or codesegments to perform the associated tasks may be stored in acomputer-readable medium such as a storage medium. Processors mayperform the associated tasks.

It will be apparent to those skilled in the art that substantialvariations may be made in accordance with specific requirements. Forexample, customized or special-purpose hardware might also be used,and/or particular elements might be implemented in hardware, software(including portable software, such as applets, etc.), or both. Further,connection to other computing devices such as network input/outputdevices may be employed.

With reference to the appended figures, components that can includememory can include non-transitory machine-readable media. The term“machine-readable medium” and “computer-readable medium,” as usedherein, refer to any storage medium that participates in providing datathat causes a machine to operate in a specific fashion. In embodimentsprovided hereinabove, various machine-readable media might be involvedin providing instructions/code to processing units and/or otherdevice(s) for execution. Additionally or alternatively, themachine-readable media might be used to store and/or carry suchinstructions/code. In many implementations, a computer-readable mediumis a physical and/or tangible storage medium. Such a medium may takemany forms, including, but not limited to, non-volatile media, volatilemedia, and transmission media. Common forms of computer-readable mediainclude, for example, magnetic and/or optical media such as compact disk(CD) or digital versatile disk (DVD), punch cards, paper tape, any otherphysical medium with patterns of holes, a RAM, a programmable read-onlymemory (PROM), an erasable programmable read-only memory (EPROM), aFLASH-EPROM, any other memory chip or cartridge, a carrier wave asdescribed hereinafter, or any other medium from which a computer canread instructions and/or code. A computer program product may includecode and/or machine-executable instructions that may represent aprocedure, a function, a subprogram, a program, a routine, anapplication (App), a subroutine, a module, a software package, a class,or any combination of instructions, data structures, or programstatements.

Those of skill in the art will appreciate that information and signalsused to communicate the messages described herein may be representedusing any of a variety of different technologies and techniques. Forexample, data, instructions, commands, information, signals, bits,symbols, and chips that may be referenced throughout the abovedescription may be represented by voltages, currents, electromagneticwaves, magnetic fields or particles, optical fields or particles, or anycombination thereof.

Terms, “and” and “or” as used herein, may include a variety of meaningsthat are also expected to depend at least in part upon the context inwhich such terms are used. Typically, “or” if used to associate a list,such as A, B, or C, is intended to mean A, B, and C, here used in theinclusive sense, as well as A, B, or C, here used in the exclusivesense. In addition, the term “one or more” as used herein may be used todescribe any feature, structure, or characteristic in the singular ormay be used to describe some combination of features, structures, orcharacteristics. However, it should be noted that this is merely anillustrative example and claimed subject matter is not limited to thisexample. Furthermore, the term “at least one of” if used to associate alist, such as A, B, or C, can be interpreted to mean any combination ofA, B, and/or C, such as A, AB, AC, BC, AA, ABC, AAB, AABBCCC, etc.

Further, while certain embodiments have been described using aparticular combination of hardware and software, it should be recognizedthat other combinations of hardware and software are also possible.Certain embodiments may be implemented only in hardware, or only insoftware, or using combinations thereof. In one example, software may beimplemented with a computer program product containing computer programcode or instructions executable by one or more processors for performingany or all of the steps, operations, or processes described in thisdisclosure, where the computer program may be stored on a non-transitorycomputer readable medium. The various processes described herein can beimplemented on the same processor or different processors in anycombination.

Where devices, systems, components or modules are described as beingconfigured to perform certain operations or functions, suchconfiguration can be accomplished, for example, by designing electroniccircuits to perform the operation, by programming programmableelectronic circuits (such as microprocessors) to perform the operationsuch as by executing computer instructions or code, or processors orcores programmed to execute code or instructions stored on anon-transitory memory medium, or any combination thereof. Processes cancommunicate using a variety of techniques, including, but not limitedto, conventional techniques for inter-process communications, anddifferent pairs of processes may use different techniques, or the samepair of processes may use different techniques at different times.

The specification and drawings are, accordingly, to be regarded in anillustrative rather than a restrictive sense. It will, however, beevident that additions, subtractions, deletions, and other modificationsand changes may be made thereunto without departing from the broaderspirit and scope as set forth in the claims. Thus, although specificembodiments have been described, these are not intended to be limiting.Various modifications and equivalents are within the scope of thefollowing claims.

1. A light emitting diode comprising: an active light emitting layerwithin a semiconductor layer, wherein the semiconductor layer has a mesashape; a substrate comprising a first surface on which the semiconductorlayer is positioned and an outcoupling surface opposite to the firstsurface, wherein light generated by the active light emitting layer isincident on the outcoupling surface and propagates toward an opticalelement downstream of the outcoupling surface; and at least one of: afirst anti-reflection coating adjacent to the outcoupling surface; anindex-matched material between the outcoupling surface and the opticalelement, wherein an index of refraction of the index-matched material isgreater than or equal to an index of refraction of the optical element;or secondary optics adjacent to the outcoupling surface, wherein thelight emitting diode has a first light extraction efficiency between 50%and 85% within a first emission cone having a first angle of 90°, and asecond light extraction efficiency between 2% and 6% within a secondemission cone having an second angle of 10°.
 2. The light emitting diodeof claim 1, wherein the mesa shape is at least one of planar, vertical,conical, semi-parabolic, or parabolic, and a base area of the mesa is atleast one of circular, rectangular, hexagonal, or triangular.
 3. Thelight emitting diode of claim 1, further comprising a reflector layer onan outer surface of the mesa shape, wherein the reflector layercomprises, in order from the outer surface of the mesa shape, adielectric passivation layer, an adhesion layer, a diffusion barrierlayer, and a coating layer.
 4. The light emitting diode of claim 1,wherein the index-matched material is butt-coupled to the opticalelement, and the optical element comprises a waveguide.
 5. The lightemitting diode of claim 1, wherein the semiconductor layer comprises ann-side semiconductor layer adjacent to the substrate and a p-sidesemiconductor layer opposite to the active light emitting layer.
 6. Thelight emitting diode of claim 5, wherein the secondary optics comprise alens having a focal point at the active light emitting layer.
 7. Thelight emitting diode of claim 6, wherein the lens is a spherical lens ora Fresnel lens.
 8. The light emitting diode of claim 6, wherein adiameter of the lens is greater than a diameter of the semiconductorlayer adjacent to the substrate.
 9. The light emitting diode of claim 6,wherein the lens is etched into the outcoupling surface.
 10. The lightemitting diode of claim 6, wherein the lens has different lens shapesalong a lateral direction of the lens, or a donut-like recess area and afocal point that are configured to out-couple different groups of raysfrom the light emitting diode within an emission cone having ahalf-width at half-maximum (HWHM) less than or equal to 60°.
 11. Thelight emitting diode of claim 5, wherein the secondary optics areconfigured to emit light having a beam profile with a substantiallytop-hat shape and a half-width at half-maximum (HWHM) less than or equalto 60°.
 12. The light emitting diode of claim 6, wherein the secondaryoptics further comprise additional spherical lenses that are configuredto collimate light reflected by a facet of the mesa shape.
 13. The lightemitting diode of claim 6, wherein the secondary optics further comprisea second anti-reflection coating on a surface of the lens opposite tothe outcoupling surface.
 14. The light emitting diode of claim 5,wherein the secondary optics comprise a grating etched into theoutcoupling surface, the grating comprises a linear array that reflectstransverse electric (TE) light at a different percentage than transversemagnetic (TM) light, and the light emitting diode provides polarizedlight emission.
 15. The light emitting diode of claim 1, wherein alinear dimension of the outcoupling surface in a plane perpendicular toan emission direction of light from the outcoupling surface is less than60 μm.
 16. (canceled)
 17. A light emitting diode comprising: an activelight emitting layer within a semiconductor layer, wherein thesemiconductor layer has a mesa shape; a substrate comprising a firstsurface on which the semiconductor layer is positioned and anoutcoupling surface opposite to the first surface; and a reflector layeron an outer surface of the mesa shape, wherein the reflector layercomprises, in order from the outer surface of the mesa shape, adielectric passivation layer, a metal layer, a diffusion barrier layer,and a conformal coating layer, wherein the reflector layer has areflectivity greater than 80%.
 18. The light emitting diode of claim 17,wherein: a thickness of the dielectric passivation layer is between 60nm and 80 nm, a thickness of the metal layer is between 80 and 120 nm, athickness of the diffusion barrier layer is between 20 and 30 nm, and athickness of the conformal coating layer is between 110 and 140 nm. 19.The light emitting diode of claim 17, wherein the dielectric passivationlayer comprises at least one of SiN, SiO₂, HfO, AlN, or AlO.
 20. Thelight emitting diode of claim 17, wherein the metal layer comprises Ag,Al, or Au, and is configured to provide adhesion between the dielectricpassivation layer and the diffusion barrier layer.
 21. The lightemitting diode of claim 17, wherein the diffusion barrier layercomprises Pt, Pd, WTi, or WN.
 22. The light emitting diode of claim 17,wherein the conformal coating layer comprises Au or Al.
 23. The lightemitting diode of claim 17, wherein the dielectric passivation layer andthe metal layer are configured to prevent resonant absorption lossesinside the reflector layer.
 24. The light emitting diode of claim 17,further comprising a p-contact on a surface of the semiconductor layeropposite to the outcoupling surface.
 25. The light emitting diode ofclaim 24, wherein the p-contact comprises, in order from the surface ofthe semiconductor layer, the metal layer, the diffusion barrier layer,and the coating layer.
 26. The light emitting diode of claim 17,wherein: the mesa shape is parabolic, the mesa shape has a height ofapproximately 1.5 μm, and the mesa shape has a largest diameter in aplane parallel to the outcoupling surface of approximately 3.0 μm. 27.The light emitting diode of claim 17, wherein the light emitting diodehas a first light extraction efficiency between 45% and 55% within afirst emission cone having a first angle of 90°, and a second lightextraction efficiency between 2% and 3% within a second emission conehaving an second angle of 10°.
 28. The light emitting diode of claim 17,wherein the active light emitting layer is arranged at a focal point ofthe mesa shape.
 29. The light emitting diode of claim 17, wherein afacet of the mesa shape is sufficiently smooth to prevent non-radiativerecombination of electrons and holes at the facet.
 30. The lightemitting diode of claim 17, further comprising ions that are implantedin the active light emitting layer.
 31. The light emitting diode ofclaim 17, wherein different atoms are intermixed within the active lightemitting layer.
 32. The light emitting diode of claim 17, wherein theactive light emitting layer comprises quantum dots.
 33. The lightemitting diode of claim 17, wherein the active light emitting layercomprises a lateral quantum barrier.
 34. (canceled)
 35. A light emittingdiode comprising: an active light emitting layer within a semiconductorlayer, wherein the semiconductor layer has a mesa shape; a substratecomprising a first surface on which the semiconductor layer ispositioned and an outcoupling surface opposite to the first surface,wherein light generated by the active light emitting layer is incidenton the outcoupling surface and propagates toward an optical elementdownstream of the outcoupling surface; and at least one of: a firstanti-reflection coating adjacent to the outcoupling surface; anindex-matched material between the outcoupling surface and the opticalelement, wherein an index of refraction of the index-matched material isgreater than or equal to an index of refraction of the optical element;or secondary optics adjacent to the outcoupling surface, wherein theindex-matched material is butt-coupled to the optical element, and theoptical element comprises a waveguide.
 36. A light emitting diodecomprising: an active light emitting layer within a semiconductor layer,wherein the semiconductor layer has a mesa shape; a substrate comprisinga first surface on which the semiconductor layer is positioned and anoutcoupling surface opposite to the first surface, wherein lightgenerated by the active light emitting layer is incident on theoutcoupling surface and propagates toward an optical element downstreamof the outcoupling surface; and at least one of: a first anti-reflectioncoating adjacent to the outcoupling surface; an index-matched materialbetween the outcoupling surface and the optical element, wherein anindex of refraction of the index-matched material is greater than orequal to an index of refraction of the optical element; or secondaryoptics adjacent to the outcoupling surface, wherein the semiconductorlayer comprises an n-side semiconductor layer adjacent to the substrateand a p-side semiconductor layer opposite to the active light emittinglayer, and wherein the secondary optics comprise a lens having a focalpoint at the active light emitting layer.
 37. The light emitting diodeof claim 36, wherein the lens is a spherical lens or a Fresnel lens. 38.The light emitting diode of claim 36, wherein a diameter of the lens isgreater than a diameter of the semiconductor layer adjacent to thesubstrate.
 39. The light emitting diode of claim 36, wherein the lens isetched into the outcoupling surface.
 40. The light emitting diode ofclaim 36, wherein the lens has different lens shapes along a lateraldirection of the lens, or a donut-like recess area and a focal pointthat are configured to out-couple different groups of rays from thelight emitting diode within an emission cone having a half-width athalf-maximum (HWHM) less than or equal to 60°.
 41. The light emittingdiode of claim 36, wherein the secondary optics further compriseadditional spherical lenses that are configured to collimate lightreflected by a facet of the mesa shape.
 42. The light emitting diode ofclaim 36, wherein the secondary optics further comprise a secondanti-reflection coating on a surface of the lens opposite to theoutcoupling surface.
 43. A light emitting diode comprising: an activelight emitting layer within a semiconductor layer, wherein thesemiconductor layer has a mesa shape; a substrate comprising a firstsurface on which the semiconductor layer is positioned and anoutcoupling surface opposite to the first surface, wherein lightgenerated by the active light emitting layer is incident on theoutcoupling surface and propagates toward an optical element downstreamof the outcoupling surface; and at least one of: a first anti-reflectioncoating adjacent to the outcoupling surface; an index-matched materialbetween the outcoupling surface and the optical element, wherein anindex of refraction of the index-matched material is greater than orequal to an index of refraction of the optical element; or secondaryoptics adjacent to the outcoupling surface, wherein the semiconductorlayer comprises an n-side semiconductor layer adjacent to the substrateand a p-side semiconductor layer opposite to the active light emittinglayer, and wherein the secondary optics are configured to emit lighthaving a beam profile with a substantially top-hat shape and ahalf-width at half-maximum (HWHM) less than or equal to 60°.
 44. A lightemitting diode comprising: an active light emitting layer within asemiconductor layer, wherein the semiconductor layer has a mesa shape; asubstrate comprising a first surface on which the semiconductor layer ispositioned and an outcoupling surface opposite to the first surface,wherein light generated by the active light emitting layer is incidenton the outcoupling surface and propagates toward an optical elementdownstream of the outcoupling surface; and at least one of: a firstanti-reflection coating adjacent to the outcoupling surface; anindex-matched material between the outcoupling surface and the opticalelement, wherein an index of refraction of the index-matched material isgreater than or equal to an index of refraction of the optical element;or secondary optics adjacent to the outcoupling surface, wherein thesemiconductor layer comprises an n-side semiconductor layer adjacent tothe substrate and a p-side semiconductor layer opposite to the activelight emitting layer, and wherein a linear dimension of the outcouplingsurface in a plane perpendicular to an emission direction of light fromthe outcoupling surface is less than 60 μm.
 45. A light emitting diodecomprising: an active light emitting layer within a semiconductor layer,wherein the semiconductor layer has a mesa shape; a substrate comprisinga first surface on which the semiconductor layer is positioned and anoutcoupling surface opposite to the first surface; and a reflector layeron an outer surface of the mesa shape, wherein the reflector layercomprises, in order from the outer surface of the mesa shape, adielectric passivation layer, a metal layer, a diffusion barrier layer,and a conformal coating layer, wherein: the mesa shape is parabolic, themesa shape has a height of approximately 1.5 μm, and the mesa shape hasa largest diameter in a plane parallel to the outcoupling surface ofapproximately 3.0 μm.
 46. A light emitting diode comprising: an activelight emitting layer within a semiconductor layer, wherein thesemiconductor layer has a mesa shape; a substrate comprising a firstsurface on which the semiconductor layer is positioned and anoutcoupling surface opposite to the first surface; and a reflector layeron an outer surface of the mesa shape, wherein the reflector layercomprises, in order from the outer surface of the mesa shape, adielectric passivation layer, a metal layer, a diffusion barrier layer,and a conformal coating layer, wherein the light emitting diode has afirst light extraction efficiency between 45% and 55% within a firstemission cone having a first angle of 90°, and a second light extractionefficiency between 2% and 3% within a second emission cone having ansecond angle of 10°.
 47. A light emitting diode comprising: an activelight emitting layer within a semiconductor layer, wherein thesemiconductor layer has a mesa shape; a substrate comprising a firstsurface on which the semiconductor layer is positioned and anoutcoupling surface opposite to the first surface; and a reflector layeron an outer surface of the mesa shape, wherein the reflector layercomprises, in order from the outer surface of the mesa shape, adielectric passivation layer, a metal layer, a diffusion barrier layer,and a conformal coating layer, wherein the active light emitting layeris arranged at a focal point of the mesa shape.
 48. A light emittingdiode comprising: an active light emitting layer within a semiconductorlayer, wherein the semiconductor layer has a mesa shape; a substratecomprising a first surface on which the semiconductor layer ispositioned and an outcoupling surface opposite to the first surface; anda reflector layer on an outer surface of the mesa shape, wherein thereflector layer comprises, in order from the outer surface of the mesashape, a dielectric passivation layer, a metal layer, a diffusionbarrier layer, and a conformal coating layer, wherein a facet of themesa shape is sufficiently smooth to prevent non-radiative recombinationof electrons and holes at the facet.
 49. A light emitting diodecomprising: an active light emitting layer within a semiconductor layer,wherein the semiconductor layer has a mesa shape; a substrate comprisinga first surface on which the semiconductor layer is positioned and anoutcoupling surface opposite to the first surface; a reflector layer onan outer surface of the mesa shape, wherein the reflector layercomprises, in order from the outer surface of the mesa shape, adielectric passivation layer, a metal layer, a diffusion barrier layer,and a conformal coating layer; and ions that are implanted in the activelight emitting layer.
 50. A light emitting diode comprising: an activelight emitting layer within a semiconductor layer, wherein thesemiconductor layer has a mesa shape; a substrate comprising a firstsurface on which the semiconductor layer is positioned and anoutcoupling surface opposite to the first surface; a reflector layer onan outer surface of the mesa shape, wherein the reflector layercomprises, in order from the outer surface of the mesa shape, adielectric passivation layer, a metal layer, a diffusion barrier layer,and a conformal coating layer, wherein different atoms are intermixedwithin the active light emitting layer.
 51. A light emitting diodecomprising: an active light emitting layer within a semiconductor layer,wherein the semiconductor layer has a mesa shape; a substrate comprisinga first surface on which the semiconductor layer is positioned and anoutcoupling surface opposite to the first surface; a reflector layer onan outer surface of the mesa shape, wherein the reflector layercomprises, in order from the outer surface of the mesa shape, adielectric passivation layer, a metal layer, a diffusion barrier layer,and a conformal coating layer, wherein the active light emitting layercomprises a lateral quantum barrier.